Growing up I was always a Vette fan (my first car was a 71 Vette which I still have), because I liked the looks of the older ones, but I always appreciated Mopar engines and the flat out tough squared off looks of the old 60 muscle cars (hence the 67 Dart I bought). I've never liked Mustangs that much, although some do look nice and most sound pretty dang good. That being said, having been a member of the local Vette club for about 10 years now the newer ones are just kind of boring looking. Everyone in the club is buying C5's and up so there's just no variety. I'm one of the youngest guys in the club and I dang near have the oldest car. The C6 is still kind of blah to me, though better than a C5, and the C7 is a step up, but once I see them all over the roads I'll probably get tired of them. I have to give Vettes credit though, my mom's 99 is just about the most pratical vehicle in the family. It's sporty and fun to drive, has tons of cargo space (coupe) so it's easy to take grocery shopping or something, and it gets 30+ mpg cruising down the highway if you need to go somewhere.
The thing I like so much about the Viper is that it only comes in one flavor, "kill". A base model Vette is nothing to sneeze at for performance, but to compare to a Viper you have to get a top of the line ZR-1 to run toe to toe. Mustangs are even worse in my opinion. Sure you can get a 1000 hp Shelby, but it still mostly looks like grandma's V6 wannabe. You can only mod and pump up the original so much before you should have really just gotten another car to begin with. The Viper starts fast and only gets faster, end of story. It's built to do what it does from the get-go. A Mustang chassis will never out-handle a Viper unless you pretty much start all over with all the changes you have to make for it to handle the performance. I've had the same dilemma with my motorcyle. I'd love to do all the engine mods I can to it to make it faster to run with sport bikes, but in the end it would be cheaper to just buy something that has the power I want to start with.