AmpliTube 4

Out of Warp, Revalver and Amplitube, this is far and away my favourite.
Compared to Warp, it is far more flexible, with more features and a wider variety of sounds. And Warp's sound is not, to my ears, particularly impressive.
Compared to Revalver, it is perhaps slightly less flexible since it has a linear rather than a modular design. To me, Revalver can also match Amplitube on simple clean sounds. But other than that, Ampitube sounds much better to me: it doesn't have that exagerated, gimicky sort of sound that I often hear in Revalver and some hardware modelling units (like the first POD units).
UI: Looks nice, easy to understand, kind of big & 3 pages long, but there's a lot to fit in there.
Sound: Very good. The effects are modeled after typical guitar stompboxes and such. The spring reverb is very nice.
Features: Plenty. Maybe the mic simulator could be a little more flexible. Some people might find the pre-amp pedals or the post-amp effects superfluous.
Docs: Very nice; they explain the routings and talk a bit about the hardware that is being emulated.
Presets: Quite a few and a good range.
Customer support: Never used it, but I'm penalizing them for their challenge-response system (didn't cause me any problems but I don't like it).
VFM: Obviously if you're comparing it to hardware, it's dirt cheap. But I think it's more reasonable to compare it to similar software. Difficult to do since nothing else quite does what it does. Its price is about what I'd expect for a plug of this quality and with these features, but these days there are so many cheap/free plugs that offer *some* of the funtionality of Amplitube (simulanalog guitar suite, green machine are of special note), a lot of people probably will probably feel that the price could be a little lower.
Stability: Some people have reported crashes or problems when using more than one instance, but I've had none. Edit: I've now encountered some stability issues. First, the plug seems to suffer from the P4 denormal problem, which by this point is simply inexcusable. Second, the plug sometimes just "gives up" and begins outputting nothing but intermittent pops, requiring me to unload & reload it.Read Review