Personally, I'd definitely go the R34 25GT-T. Amazing looking car. In black or white, take your pick. The R34 is larger, and has a slightly more roomy interior.
Stacks of mods for both cars, so that's not a problem.
I can't say too much handling wise, but both cars could be made to handle well with basic suspension upgrades (Whiteline's handling kit/sports pack/works).