Back when I bought my Z28 in '98, I had quite a bit of contempt for Mustangs and Ford in general. At the time I'd never think I'd own one, let alone two. Obviously my viewpoint has changed over the years. Come to think of it, I'm not really crazy about the majority of GM's, Ford's or Chrysler's lineup as it stands these days, aside from their V-8 (or 10) powered RWD vehicles that aren't trucks or SUVs. Otherwise, I'd be looking at Germany, Japan or South Korea for my automotive needs.
In my opinion, with so many Camaros and Mustangs built in so many variations and owned by so many people over the past 40+ years, to denigrate either car or their owners is to paint them with a rather large brush and isn't really fair. Also, bashing either one simply because they happen to be common on the roads is pretty ridiculous. Both of these cars are and have always been marketed as affordable sports cars for the masses - if you want exclusivity, look elsewhere (or buy a ZL1/Boss/GT500).
With regards to looks, it's all subjective. When I was considering both cars to replace my '06 GT, looks hadn't really entered into the equation. IMO, both can be quite dull on the outside; a light-colored base V6 Mustang or LS Camaro for instance, doesn't really do anything for me. On the other hand, I do like a clean Brembo-packaged GT with factory HIDs in a darker color without the fake side/hood scoops and window louvers that are all too common on today's Mustangs. Similarly, a darker-hued SS/RS would definitely grab my attention. If I saw a Boss 302, ZL1 or GT500, I'd probably have to ensure that there's no drool coming out of my mouth...
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Gone: 2011 Ford Mustang GT Premium (Sterling Gray Metallic, HID/Security Pkg, Brembo Pkg, 6M)
Current: 2015 Dodge Challenger R/T Scat Pack (Ivory White Tri-coat Pearl, Driver Convenience Grp, Leather Interior Grp, 8A)
Future(?): 2018 Chevrolet Camaro 2SS (Hyper Blue Metallic, NPP, 56R, 6M) or Ford Mustang GT Premium (Lightning Blue Metallic, Active Exhaust, Performance Package, 401A Package, Spoiler Delete, 6M)