I just got the new Amplitube Fender last week and also bought a SansAmp PSA-1 recently (hardware). Played with both yesterday, and I actually think the Amplitube Fender sounds best of the two (mainly doing Twin Reverb) ...

But maybe most of the others here are talking about heavily distorted amp simulation? I have a feeling the cleaner amps are easier to simulate?

In the real world I also prefer a Twin Reverb and use an overdrive pedal (Fulltone or T-Rex) for distorted sounds. And so far none of the amp plugins can compete with this. But adding the same hardware pedal before a clean plugin amp works great.

Nevertheless of all the amp plugins I have tried Amplitube is the best, but still maybe not good enough ... ?