I have recently aquired a few new amp sims lately and thought I would share some thoughts.  I currently have GR5, TH2-Producer, Amplitube 3, and Peavey Revalver HP.  I have had a few hardware amp sims over the years as well.
 
- First, I greatly prefer the rack-style interface of GR5 and Revalver HP over the stomp/amp/cab/rack style of Amplitube 3 and TH2.
a) It's nice to have everything on one page.  Most patches consist of maybe one pedal in front of the amp and a reverb after.  If I am doing something like balancing how much gain I want coming from my OD pedal vs how much comes from the amp, it's a lot easier to do without switching between multiple tabs.
 
b) Maybe I want to see how the chorus sounds after the amp instead of before it.  In GR5 I can move anything anywhere in the chain.  In A3 I can't.
 
- TH2 annoys me because the signal flow on the pedals goes from left to right.  In the real world, the overwhelming majority of pedals are designed so the signal goes the opposite way.
 
- The pedals on A3 look and sound great, but I don't like how on some of them, it's hard to see the markings on the knobs.
 
- A lot of people say they like A3 for amps and GR5 for effects.  I agree.  It did not take me long to set up an A3->GR5 patch preset.
 
- I am surprised that A3 does not have a treble booster.  Also surprised that the core version does not have a boost pedal (it comes with Slash)
 
- Orange amps must not be that hard to model.
 
- One of my favorite amp models is still the Crunch from the Boss GT series.
 
- I also really like the Peavey Classic 30 model on Revalver.
 
- Thanks to the A3 group buy, it will take me a really long time to fully appreciate all the options I have available to me.
 
- A lot of the time, my favorite sims are the house brands.  For example, on the J-Station, my favorites were the J-Drive and J-Solo.  Maybe there's something to the idea of making something that sounds what you want an amp to sound like as opposed to making it sound like a specific amp actually does sound like.  Perhaps this implies that I need to check out S-Gear.
 
 
 
 

I prefer A3. In particular the Fender package. I have Revalver MKIII and don't like it at all (maybe the new version will be better). I tried the TH2 demo (full version) and it sounded pretty good. It's a lot better than the amps included with TH2 producer, but I haven't bought it. I've tried S-gear a couple of times and just don't get the hype. It's pretty good, but very limited and I like Amplitube better. I think it's the use of the Irs. I have several Redwirez cabs, but always prefer the cabs in Amplitube. GR5 I would like to have. I'm always lurking around at KVR looking for a good deal. Thanks for changing the subject back to guitars. I've been in drum sampler mode for too long!

I have PodFarm (which I easily get great sounds out of), TH2 full version, GR5, Amplitube 3.

I've evolved in my opinion of which one I like the most. I get what I want and need now mainly from Amplitube. It seems to be set up the way I would envision the signal flow to go.

If I had only one of the four, any of them, I'd be satisfied. I've just migrated to mainly working in Amplitube. I like how it looks and sounds, and the most samples and tutorials are available on Amplitube compared to the others, which has accelerated my ability to harness what it can do.

I have Amplitube, Pod Farm, Guitar Rig, S-Gear, Waves GTR, Avid Eleven, Logic's Amp Designer, Revalver HP,  and anything available for Mac OS I've most likely tried. I also own ReCabinet and MixIR and tons of cab impulses. I've worked with amp sims (software and hardware) since 99 or 2000. I also own a POD 2, a POD HD and a Line 6 Spider.
 
I've rarely been consistently satisfied with any one solution for too long. POD HD would be the closest. 
 
The one thing that's finally freed me from the endless hours of tweaking and re-recording and eq-ing and compressing only to start from scratch the next day is the little Randall tube amp I bought recently. That and a SM57 and I haven't looked back. I can focus on the music because it always sounds adequate and, more importantly, I don't have to try to make it sound like a real amp. 
 
Since it's only 5 watts, I can push the volume all the way and get that sound.
 
The funny thing is that, of all the things I've tried, it's one of the least expensive solution - same price as Guitar Rig. My new best friend, really...
 

 
 
 
 
 

I have GR, Amplitube, TH2 Full, TH2 Producer, Peavey ReValver, and some random freebie amp vsts. Hardware wise, I have a Boss GT, Line 6 POD 2.0, Line 6 HD500, and an old Alesis Quadreverb GT!. I find myself using TH2 Full and Amplitube the most out of the sims. Although, I am working a lot here lately with the HD500 in stereo, straight to the interface.
I have to admit as a guitarist I am in a love hate relationship from day to day with all of this stuff. I still love the sound of my two Fender Concert amps cranked with a few old Boss pedals for dirt and an old Roland Jazz Chorus 120 head pushing an old Fender bandmaster bottom wired for stereo for clean! Alas, the old ears can't take it anymore. LOL!

Rain
I have Amplitube, Pod Farm, Guitar Rig, S-Gear, Waves GTR, Avid Eleven, Logic's Amp Designer, Revalver HP,  and anything available for Mac OS I've most likely tried. I also own ReCabinet and MixIR and tons of cab impulses. I've worked with amp sims (software and hardware) since 99 or 2000. I also own a POD 2, a POD HD and a Line 6 Spider.
 
I've rarely been consistently satisfied with any one solution for too long. POD HD would be the closest. 
 
The one thing that's finally freed me from the endless hours of tweaking and re-recording and eq-ing and compressing only to start from scratch the next day is the little Randall tube amp I bought recently. That and a SM57 and I haven't looked back. I can focus on the music because it always sounds adequate and, more importantly, I don't have to try to make it sound like a real amp. 
 
Since it's only 5 watts, I can push the volume all the way and get that sound.
 
The funny thing is that, of all the things I've tried, it's one of the least expensive solution - same price as Guitar Rig. My new best friend, really...
 

 
 
 
 
 

I have a HD500 and DT50. I'm going to be recording with it some as well.

One other thing I think is weird concerns the component presets.  GR5, A3, and Revalver HP all have component presets where you could save a setting.  For example if you had certain settings that you liked to use on a particular amp sim, you could just call up the component preset.  Perhaps you insert a twin in the chain - you could quickly choose whether you want the country setting, the surf setting, the pop setting,  the blues setting, etc.  Or if you insert a delay you could pull up a setting for doubling, one for tempo delay, one for long echoes, etc.
 
The odd part is that GR5 actually has some of these effects presets defined and available.  On A3 and HP, you can save your own, but they haven't given you any starting points. 

clintmartin
I prefer A3. In particular the Fender package. I have Revalver MKIII and don't like it at all (maybe the new version will be better). I tried the TH2 demo (full version) and it sounded pretty good. It's a lot better than the amps included with TH2 producer, but I haven't bought it. I've tried S-gear a couple of times and just don't get the hype. It's pretty good, but very limited and I like Amplitube better. I think it's the use of the Irs. I have several Redwirez cabs, but always prefer the cabs in Amplitube. GR5 I would like to have. I'm always lurking around at KVR looking for a good deal. Thanks for changing the subject back to guitars. I've been in drum sampler mode for too long!

I'm sold on SGear now, and it is precisely because it is a bit limited.  The amps models are absolutely top notch, and the cab impulses are amazing.  By focusing on the heart of the sound and on fewer options, I always find tones I really like.  My main problem with Amplitube and GR is that there are just too many options, and too many ways to screw up the sound.  I tweak until I have lost all view of reality.  S Gear makes me appreciate the sound of the amps and I tend to tweak less and play more.  

I have been patiently waiting for a Sale..for a year...nothing...

I'd really like to have S-Gear...sadly, I can't reach it....and it's a want...
not a NEED...as much as I'd like to call it a need...LOL

The thing that keeps me from endlessly tweaking is all the years of playing through certain amp setups with certain effects. I don't really try to find a groundbreaking new sound much. I try to stay focused on what hardware amp I would use for any given project. When I first got in to the sims there were so many options and of course I ended up learning inside and out how to operate the software. But when push comes to shove there is really to me three basic building blocks for great guitar amp sound. 1 great clean sound, 1 great crunch sound, and 1 great distortion sound. In the sims, I try to emulate what amp sound I need building from those key elements
I bought a Boss GT5 when they first came out. There were tons of good sounds in that unit. I sat down and built 5 settings in 1 bank for me to use live. All my guitar buds would come out and marvel at the blue box that had so many great settings in it while all night I used 5 sounds and no more. If you can strip it all down to dry amp settings and just concentrate on getting that as close as you can, then you can be sparing with the FX that you add and it should be fairly easy to get what you want. I still like pulling out my POD 2.0 because it is all about getting the amp sim first and you only have very few FX to muck up the tone with. It is very overwhelming when you throw in mic sim, cabinet settings, 150 FX, etc.
What the sims brought to the table with me is the ability to swap amps for different settings. Most players have one amp they play through all night long and they use stomps to augment the sound. I love the sims ability to let me play through the Twin for clean, switch to Marshall for crunch, and switch to Soldano for distortion. I use the amp settings just as if the hardware unit was there. I hardly ever use a stomp crunch or distortion box. I try to approach it as running through a 3 amp setup. Any other presets I write have some FX added. I would have to pay a cartage service out the but to have all that hardware lugged around. It's great to just throw the laptop or my HD500 in the truck and go.