I have been using Amplitube 4, some of the time. when I'm running PreSonus Studio One or Reaper that's what I usually use, although Studio One has it's own amp modelling called Ampire and I do use that too.
In Cubase I usually use the built in VST Amp Rack, especially as being a bass player I find their emulations of bass amps to be better.
I'm having a look at Amplitube 5 now, review to follow. Unfortunately first impressions, which let's face it are very important with software, are not good. It's flaky, slow, the UI has areas of dark grey labelling on a black ground, and worst of all I cannot get some of my previous gear, including the Engl Powerball amp which was my favourite guitar model.*
As they patch it (one release has already gone live) things may improve. We shall see!
*LATER: I've found the Engl Powerball, purely by accident. In Amplitube 4 it is called 'Engl Powerball', which given that's what it is makes sense. In Amplitube 5 it is called 'Powerball', which doesn't make sense because if one searches for 'Engl', which is what I did, the search returns no results. I bet this sort of pointless renaming of gear is what is causing a lot of the reported problems.