There are probably a thread or two on this topic already but let me put in my 2 cents.
Gen 1 cars being the first Vipers have the least horsepower and creature comforts. They were all roadsters and have plastic windows and tend to leak. Many don't have A/C. Yet to many they are sentimental favorites because they started the whole Viper legend. There styling was "out there" for the time and they still look good today. Gen 1s had side exhaust. I've never owned a Gen 1.
Gen 2 cars including the new for 1996 Coupe were a bit more sophisticated with glass side windows and A/C. Horsepower also jumped to 450. Later Gen 2s also added ABS. Some of the Gen 2s had forged pistons which stand up better to mods, other Gen 2s don't. I can't remember which year they changed but I want to say 1999. The Gen 2 roadsters still leaked water so driving in the rain is not recommended, at least by me. Gen 2s also added the Naca duct on the hood. I owned a 1998 RT/10. Styling of course was still much like the Gen 1s but without the side exhaust.
Gen 3 cars beginning in 2003 were significantly better driving cars than Gen 1 or 2s. Horsepower was jumped to 500 (or a little more based on newer testing standards). All 2003-2005 Gen 3s were full convertibles with folding tops and power side windows. They were tighter and are plentiful in the used market at reasonable prices. In 2006 they launched the coupe. Many people didn't care for the Gen 3 styling as compared to the Gen 1/2s. I wasn't crazy about it initially but I really like it now. The coupe is awesome looking to me. The convertibles no longer leak water.
Gen 4s started in 2008, there was no 2007. Gen 4s have 600 HP and a beefier trans and a different rear end. They also get a swinging oil pickup and are drive by wire. Other than the hood, which is more aggressive on the Gen 4s, they look pretty much like a Gen 3. There are also more wheel choices. Exhaust changes make the Gen 4s cooler inside than previous Gens, including the Gen 3.
Bottom line. The answer to your question depends on several factors. Which style do you prefer? Do you want a convertible or a coupe? All Gen 1s are convertibles, Gen 2-4 give you a choice. How much do you wish to spend? If money is no object I would say get a Gen 4, they are simply better. If you prefer the Gen 1/2 style, I would get a Gen 2 because they have more HP are newer and to me the hood with the duct is cooler looking. If you prefer Gen 3/4 styling but don't want to step up to the dollars for a Gen 4 then a Gen 3 is a good choice.
Either way Viper ownership is something special so good luck with your decision and don't forget to join the VCA when you get one. Also when you do you should consider attending VOI 11 in Utah. VOIs are awesome.
