My 3rd car was a '67 fastback, 289, Autolite 4-bbl, automatic. It wasn't hot, and it wasn't nearly as nimble as my Datsun 2000 had been, but it was fun enough. I sort of beat the shit out of it, and I sold it for a pittance when I went into the Army in 1979.
I'd take it now in a heartbeat, but I really do like the '65-66 body style better. It was the cleanest, freshest styling of all the Mustangs. Almost everything since has been derivative of it. The exceptions would be the early Fox-bodied Mustangs, and they just didn't look all that great, IMO, in addition to not looking much like Mustangs.
That has it's benefits. Mustangs have always had a certain look, while Camaros never have. But it does limit what Ford can do with the styling 56 years later.