My first printer was a Prusa i2. The threaded rod frame is a real pain but once I got it put together it worked great. The show stopper for me was the build height. Because of the design, you are limited to about 5.5 inches of build height. You can still make plenty of stuff but I wanted to go higher. There is really no way to mod the i2 (nor the two you list above for that matter) to increase the build height.

The i3 will give you almost eight inches of build height and be much easier to construct. Makerfarm sells kits for under $600, less the power supply and glass for the heated bed. You could also build the frame yourself and get your buddies to print the rest: http://reprap.org/wiki/Prusa_i3_Build_Manual

Good luck. I'm on my 3rd printer in a year. It is very addicting and a great hobby.

Cheers,

KDog