Sidroe
I have Amplitube, Guitar Rig, Re-Valver, and TH2. Bang for the buck, Th2 wins out most of the time. It is more like the Swiss Army knife of sims because of the FX included. I'm not having to jump around after the amp sim and add a bunch of FX which means jumping around between more windows to edit. At least in TH2 everything is in the same window and dead easy to edit. That's pretty handy when you are working at a pretty fast pace and need to move on.
I am very impressed with BIAS but most all the demo sounds have been shredding. I do a lot of jazz and ballads and I am wondering how BIAS translates in to the more subdued and clean sounds. I'll probably give it a try. Although, I have had my eye on S-Gear for a long time.
Out of Amplitube, Guitar Rig, and TH2, TH2 would be my pick and has been my go-to so far. I never understood the appeal of Amplitube. I thought it was ok for over the top effects laden sounds, but as a straight amp, it always sounded fizzy to me.
A shame that BIAS has geared their demos to the shredder market, because while I like to "shred" from time to time when no one is looking, my ideal sound is that clean/slight breakup type sound. BIAS is great for that.
I've only tried the S-Gear demo and for clean sounds it's great, I personally haven't found it useful for much more than that, but an S-Gear/BIAS combo would fill all my guitar tone needs.