KeyStage seems more flexible , (if you want to use a lot of ios instruments,) has a very powerful midi filter and transform options. I've tried it with many ios apps haven't found any important issues, it sends a midi prg chg to recall the settings in your ios apps. Still a work in progress , but right now it's more useful than the other 2 apps for an ios based rig
From a very quick perusal, iMidiPatchbay seems easiest to use, it can display charts, and it works even on an iPhone. Biggest limitation seems to be that it supports only up to 4 zones.
KeyStage seems more flexible, but more complex. Very notable feature: seamless sound transitions when switching patches. (Does anyone else have that?)
Camelot Pro seems more limited in which other iOS apps it will work with compared to the other two. It does display charts, though. From what I've seen so far, its biggest advantages seem to be that it is cross-platform; and as RG said, you can control a lot of its functions over MIDI from your controller; and probably most interesting to me, they are building in specific hardware integration. So for example, if you're using a supported board, instead of having to look up the MSB/LSB/PC numbers to enter to call up a specific sound on your board and/or type the name of the sound into the app (as you would with the others), CP already knows what numbers are associated with which sound and it can retrieve patch names from the boards so you don't have to type them in. It also gives you more on-screen control of various parameters of the sound and the individual parts within a multi-part sound. The usefulness of this feature, of course, depends on using it with those specially supported boards, but more will be added.
So, to any of you who have used these... Did I get that right? What other noteworthy differences have you found?