If I remember correctly (and I could be wrong) the Shelbys have independent rear suspension while the "regular" Mustangs have a live rear axle; not sure about the Boss 302 or the Laguna Seca.
I have a 2012 GT and it's more than enough car for the street and the handling is fine. Getting a little drift on the on-ramp is a blast and even the pedestrian GT will EASILY break the rear end loose in 2nd gear (I have the 3.73 rear end). Yes, a little axle tromp happens over bumps in a turn, but that adds to the fun.
FWIW, my MUstang is a lot more fun to drive than either the WRX or the Legacy GT I had previously (both AWD and both with independent rear suspension). For my level of (or lack of) skill, the live rear axle is not a limiting factor.
Honestly, I think the Camaro is slightly more attractive than the Mustang, but also a bit more "cartoonish". They're both great cars, but Ford seems to be more interested in selling Mustangs than Chevy is in selling Camaros.
Think about it, an attainable Ford with 650hp on pump gas with a factory warranty. Wow.