this is a personal preference thing. both cars can be made fast, and looks are subjective. the reality of the matter is that even the 'newest' camaros are 6-7 years old---you're not getting a new car. and if you're looking at mid/late 90's mustangs, the same rule applies--you're buying a 10 year old car. you could be lucky, and it could be in great shape. or it could have been abused to shit, and turn out to be a complete rattle box p.o.s.
at the same time, i hate the newer style mustangs. i vote neither. my latest car purchase was a GTO, and if i could do it again, i would have bought a G8. i'm on the prowl for another car, and its neither a mustang nor a camaro.
the only appeal to these cars, is that they can be had for cheap, and made to go fast for cheap. as for quality, its a toss-up--line up 10 random 1993 mustang GT's or camaros and you could imagine the variety of driving experience you would get.