Since the Adobe apps aren’t yet optimized for the Intel machines, if you’re really going for top speeds see if you can find an “old” Quad G5 and max it out with RAM, at least 4GB.
If you want to future-proof yourself and don’t mind a bit slower execution (because of the emulation) then a Mac Pro with 4GB RAM is definitely the way to go.
If you don’t need all that power and want something portable, go for the MacBook Pro 17″ for the screen real-estate. It’s worth it. I know the MacBook Pro is my next machine (if Apple doesn’t drop something extraordinary new tonight, that is).