They both suck equally well.
I spent 2 weeks evaluating the latest Beta after seeing the IDE at ESC in San Jose. I'm very disappointed, not much works right. On the first computer I installed it, a laptop 2.2Ghz, 2Cpu, 2Gb, it took over a minute for the IDE to come up. On the second Computer 3Ghz,2Gb,2cpu it "only" takes about 25 seconds.
I tried to convert a Studio4 example project from AT90USBKEY. The import worked without a problem, but the project was completely confused, compiled and linked the same file multiple times. I ended up copying the Makefile from Studio4 and manually updating it.
Code Editor is a pain to work with, Still no code formatting, indenting continually screws up, lacking code folding, no way of opening include files from editor.... Lots more where that came from.
Such a disappointment -- I'm going back to Eclipse IDE and deal with AVRDUDE instead, sad as that is.