Camaro's trunk is a tiny mail slot compared to the Mustang and you can't see shit out of it from the driver's seat. The upper tier Mustangs have a far nicer interior and feel a lot lighter on their feet than the Camaros.
I've always liked GM, but I'd buy the Mustang over the Camaro hands down.
Being a Chevy guy and bleeding Chevy orange we bought a Mustang. It's the V-6 one but I'll say this....put the two side by side and compare them, fit, finish, materials, paint in areas like under the hood. exterior paint on the plastic transitions to metal. The plastic feel of materials in the dash, interior leather feel. I like the Mustang more. One funny thing I never thought of was the ambient/interior lighting options the Mustang has are pretty cool. You can adjust the dash light, colors to custom settings/colors.
The sound system and the sync systems kills what GM has to offer and you set the system to text you system (car) health reports to your phone. My wife streams music from her phone easly, when the phone rings it's an easy answer and you can have a number of phones programmed to be used all hands free for whom is driving, it dials totally by voice and does text and reads your text and you can do it all with steering wheel and voice commands.
The ride, the suspension, the quality of the build have been great for us. This car will cruise at 85 MPH and return 26 MPG all day long!! I have driven it for many many miles and the seats support you well. In the end we bought our Mustang V-6 fully loaded except for the glass roof, shaker 1000 system and navigation for almost 4K less than mid range optioned Camaro. I was able to use a Ford X-plan buyer plan for discount. Gm would not honor my GM discount for the Camaro....if they did it would have been about 3K less in comparison but still more than the Mustang and with less options.
Engine and drive train, I think they are equals both are just flat awesome and the new 5.0 pretty damn nice but an LSX is bad ass also. The IRS in the Camaro is more advanced but the Mustang holds it own and in ways I think is little more fun to drive in that regard.
I would also suggest you check out a Boss.....I drove one and it's a fucking awesome ride!! Nothing in the Camaro line up compares $$$ for $$$$.