I was actually contemplating an 09 Cobalt T/C. I found one for $17 with 10k miles on it. I went and test drove it; pretty fast. The trans is a little clunky, but overall, a great compact turbo setup. It has a completely different suspension setup than the 'lesser' cobalt coupes; and it shows well.
Then I found a used '10 Camaro 2LT with 4k miles. Drove it and damn, with the IRS and LSD with the 6 speed.... It's just way more fun to drive. I ended up getting it for a badass price; about 22k; so yes it was $5k more expensive... but it was 1 model year newer, had leather & heated seats, remaining warranty, and way more badass 19" rims. But on any given day, when I see it; I know that it, in every aspect, is better than a Cobalt. Any Cobalt. I don't care if it has twin turbos and ostentatious looking front slicks with N2O. It's a Cobalt; and there's absolutely nothing wrong with that; I almost bought one. It's just not a Camaro.
As far as the OP's question; stock vs stock, the Cobalt SS/TC will win. Mod vs mod? I honestly think it depends on quality and knowledge. The aftermarket for the cobalt has plenty of options; the Camaro as of yet is slowly trickling in performance parts. I think it really is who you are; and Im not a sport compact guy. The sound of a 4cyl exhaust makes me want to
I get the whole dont compare NA to FI, but the OP was just talking stock vs stock; and a Cobalt will win.
But its still not a Camaro. I mean... look at them:
