S-Gear is my go to amp sim, but I've also been using the full version of TH3 and I sometimes use GTR Rig, mostly for the effects. 
 
S-Gear -
https://sites.google.com/site/phoenixtaiji/music/content/silkThread.mp3
 
TH3 Full
https://sites.google.com/site/phoenixtaiji/music/content/GoldenHour.mp3
 
 

Another vote for S-Gear here. Fender and Marshall sounds are it's specialty ;-)

I'm also going to suggest S-gear

Thanks for all the comments, I leanerned some things and had some things confirmed. 
 
I should have mentioned that I have TH3 full (recent Cake sale), and Amplitube 4 (iRig sale).
 
TH3 has a ton of stuff, but many of the amps are high gain weirdos that I am not familiar with.  For some reason most of the presets have a Ross compressorset to an unusable setting. (Thanks YouTube).  I find the interface on TH3 to be a bit Byzantine.  I have to give a shout out to Overloud including a DC2, one of my favorite pedals. 
 
I got Amplitube 4 Deluxe on the current sale for $100 with an interface thrown in.  The Marshalls, having been most recently updated, seem to be pretty good.  I had some IK points to get the Vibroverb amp and cab and like it as well. 
 
I also like the user interface, it seems a bit more immediate. 
 
I also have Waves GT3, and haven't even given it a spin.  I have some work to do. 
 
I suppose part of the challenge with sims is learning what each does well.

I have to throw in that I almost always use the Fender Collection in Amp 4. I own most of those "real" amps and the sims in Amp 4 are VERY close to them. Also, the Amp 4 Marshalls are very good. I have the Jimi Hendrix Collection and it is very good. I don't use shred or metal tones very much but if I did the Mesa Boogie Collection would be next on my list. I have to add that I acquired the Z-Wreck sim a few months ago and it kills!

Sidroe
Amplitube 4 and TH2 and 3 for in the box. Threatening to get BIAS. Quick and dirty live or sessions finds my POD HD500X direct to the board or usb to the computer with the Spdif set for clean to a separate track. Making the jump to Helix shortly.

You're going to like using Helix.
The UI is amazingly simple/powerful
The latest Marshall and Mesa Mk IV models are really good
 
If/when you pickup Helix, go here and download my (free) Friedman 2x12 cab IRs.
http://www.studiocat.com/temp/Friedman_2x12_cab.zip
With numerous mics/positions... the collection works well for nearly anything.
 

Does anyone have a favorite sim for VOX amps?  I'm currently favoring Amplitube for Marshalls and Fenders.

No mention of TSE X50? SHAME.
 
Really nice 5150 simulation, and for $70 it's impossible to go wrong.

I'm going to have to say S-gear too. I hope 3.0 comes out soon.

Although this is not as full featured as the bigger amp sims out there, Brainworx RockRack Pro is very good (IMO) for rock/metal tones straight out of the box......of course, YMMV. Definitely was well worth the $29 deal they recently had......never would I even consider it at the current price of $249.