Blur/Sense/TW are replaceable with 3rd party launchers, if the mfg UI is an issue for you.
The GSIII will have new radios, so it remains to be seen what, if any issues turn up. My guess is it will be negligible this time around, if not non-existent. Purely speculating, of course, I could be proven wrong with this one.
If you are going to root, etc, I've rooted and ROM'd Samsung, HTC and Motorola, and Samsung is by far the easiest, and has a great dev community, especially for their high-end devices.
And despite what others opinions and subjective rantings might be, I happen to love Samsung hardware, I think they make the best looking phones in the business. Even though the RAZR line is thin and fairly lightweight, I don't like the look and feel of them in my hand.
So if you have not guessed, my vote is for the GSIII.