Acid666

Really depends what you want. Both have motors that are easy to make more power out of. But if you're looking to autocross, you can be really competitive with a C5Z with just a few mods.
Even stock with my 02 Z06 I was climbing the top of the Raw and Pax charts locally. If you're looking to drag or bracket race, I'd just keep what you've got. If you're looking for more track duty, the C5Z is hands down the best bang for the buck that you'll find right now. I got mine more for a fun weekend car, and wanted more speed for highway pulls, but as I got more and more into autocross I find that I don't really care about that raw power any more. I'm currently in the market for an old NA/NB Miata for my wife to autocross so she can stop wearing my tires down.

So think about what you want your car to do. You can be super competitive with just tires on a stock C5Z at the AutoX.

ArmchairArchitect

Depends how much you care about handling and having a proper sports car. Trans Ams are muscle cars, not sports cars, and have good power but can't handle (poor weight distribution, heavy, suspension, ride height, etc.).

Personally, I have a 94 Mustang Cobra (muscle car) as a primary driver, and the C5Z as the toy. I love both but the C5Z is hands down more fun. There's more to life than straight line acceleration.

C5 4me

Not many T/A around in good shape & yours looks nice!

Route99

You have a very nice TA! I echo the suggestions of 001pewter, acuevo, Vetteman Jack, C5 4me and others I may have missed. If you can do it at all, I'd keep the TA and try to find a way to pick up a C5 - if not now, then when the Trans Am is paid off.
I wish I'd held on to one of mine. .
If you can only have one, then yeah, I'd say go with the C5.