I got the 12" and wow

But it is my first Mac so if you had macs before you might not be as impressed

The 17" looks huge but very thin the 12" is probably too small if you like big screens so the 15" might be the answer but they all have a clever trick up there sleeve since they can use an external display but not mirrored but as a dual head which is very good for me as the laptop goes to my left. That runs Itunes or something background and the moniter in front of me with safari etc running on it using the bluetooth keyboard and mouse.

The 12" is meant to be the hottest of them and mine is the 867Mhz and i got no real problems