I had the same difficulty chosing... The dynamic is slightly cheaper and comes with the dual zone climate and rear electric windows, which you don't get on the sport (unless you pay as I did), but I just found the whole dynamic interior a real let down with its flat front seats and 'technotweed' fabric - just didn't look right compared to the stunning exterior, and lets face it most of us spend more time looking at the inside than the out!
In terms of driving I don't think there's much between them, slightly harder ride from the sport, but it's not uncomfortable (no aches or pains after the wekk I've just had - 3,000 touring the alps and italian lakes). If your're worried about the hard ride, just don't specify the 18" wheels! As for Fenton JD 's comments, well, I couldn't agree more!