I've never been a big fan of Amplitube or any plug-in dostortion really.
When i do have to use a plug-in, i find myself going to the old Sansamp PSA-1 quite a bit.
IMHO:
Amplitube - not so good
Rock Amp Legends - awful
Amp Farm - pretty good
Sansamp - also pretty good
Guitar Rig - awful, and way to DSP hungry
Eleven - Very interesting, but i havent heard it enough yet.