Some quick thoughts on a few of them, with an emphasis on your request for pros/cons:
GTR
Pros: Stupid fast, instant street-racing cred upon purchase, can immediately start calling out everyone from roll or dig, easily modified, can make ridiculous power/numbers/gains, not as expensive as a Gallardo, about as expensive or less so than the 997TT
Cons: More expensive than a C6Z or the CTS-V, it's an automatic (which is a con from the "I'm a real driver and I like to shift shit" audience; auto could be perceived a pro from various other angles), is (at least to me) not as aesthetically pleasing as a 997TT or a Gallardo
Gallardo
Pros: Most exotic of the bunch, most unique, will get the most looks, will get you laid by girls more often (whereas GT-R will get you laid by fanbois more often), arguably the most aesthetically pleasing of the bunch, uber fast, can be made to be light-speed fast and essentially untouchable on the street with the right package (read: see UGR, not CTD)
Cons: Expensive as fuck for just about everything, right? Also, what about those Lambo elitists that will say you bought an entry-level Lambo? Not that I'd care, or most people would care, but there's always that one elitist lurking around, waiting to pounce on whatever insecurity you might have.
997TT
Pros: Aesthetically pleasing (perhaps even better looking than the Gallardo), proven platform, relatively reliable, not as expensive as the Gallardo (or so I would imagine), will get plenty of looks, uniformly well-received by both chicks and car guys, has good mod potential, good resale value
Cons: Expensive because, well, it's a Porsche. Less unique than a Gallardo, maybe even less unique than a GT-R.