the ZR is a much better trem, especially when you remove the ZPS from the back. But it doesn't have as much range, but that's probably due to the thin S series body. This is the trem i use, and it holds tuning very well. But if not setup perfectly, it just eats through strings. (but this might be the same with all trems?). The ZR2 removes the arm socket weakness that the original ZR has. I've had to replace mine, but it's a cheap easy fix.
The Edge 3 would be a decent trem if it was made of more solid materials. The knife edges wear out on those things quick and lose tuning. But you can do a direct drop in with an Edge-pro. So you could buy the Edge 3, wear it out, then put in a very good Edge Pro in there.
I think I will probably buy an Ibanez S then. All I really want the trem to do is raise half a stem, and dive a whole step or so. I was thinking about a Fender strat, but I really like Ibanez and Floyd Roses.