You could get a Roush Mustang, I don't know much about them, buy from what I know, it's a GT mustang, with upgraded high performance racing suspension, engine modifications including a super charger, and a body package. Roush has been building Mustang race cars since the 60's. Supposed to be better then a Shelby.
the boss is the best of these because of its sport tuned chassis and 444 horsepower. it also has a great history behind it and is one of the most notable mustangs ever built. the base model mustang offers good horsepower (305 hp) and great gas mileage (up to 31 mpg), so i would say it is the most sensible of your list. now, the most recognizable mustang ever built is the shelby gt500. it is expensive for a mustang ( 50k), but it is all worth it. it offers more horsepower than the renown boss 302 ( 550 to be exact), and it has a very efficient supercharged 5.4 l v8 ( about 19 mpg). lastly, the one that takes the cake starts out as a mustang before it is saleen tuned into the 475 hp, supercharged, 5.4 l v8 engine s281. even though the horsepower is lower than the shelby, it makes up for it on the streets. it has all the customizations to make it out on top. it is very well tuned for performance and is a great find. a race between this and the shelby would be great (and very close).