When I did my original review of the JamUp iOS amp sim I found it to be equal in sound quality to AmpKit. Having used it for practice more since I’m willing to say that JamUp’s simulations are better than those in AmpKit, I find them more organic and that they respond more like a physical amp to dynamics in playing. But don’t take my word for it, here’s a video of Jeff Loomis and Keith Merrow showing what you can really do with JamUp: