It's a personal preference thing really. The TTA is like driving a Corvette, low slung with the fender peaks at the corners of your eyes, handles really well, easy to maneuver, sporty, flashy, you sit low and feel like part of the machine. But it rides harsher, is a bit noisier and takes a little more effort from you.
The Buick is like sitting in church, smooth and quiet, doesn't handle as well but takes little effort to drive. If you have a T-Type Regal like me it goes totally unnoticed by everyone other than enthusiasts but I'd imagine a GN gets a fair amount of attention.
I think this is why a lot of people own both cars. The Buick is when you want to go fast without alot of fanfare or want to take the family out and the Trans Am is when you feel a bit more aggressive and want to be more involved. The TTA is the "blood and guts car" and the Buick is the "smooth performance car". That's my take on it anyway.