Hypothetically, which car would you rather buy?

It has always been a long term goal/dream of mine to purchase a sports car and spend the next 10–20 years doing work on it. I’m from a car family (like, car designers) so its in the blood, and I’ve worked with/on cars for a long time (though not so much recently).

For the longest time my plan was to purchase a Toyota Supra (a 93–98 model) that was in rough condition, and over the course of a lot of years dump $50–60k and a lot of man hours into to make it into an incredibly nice/fast car. On the pro side, a lot of people like to upgrade these cars and they made a bunch of them (relative to most sports cars), so parts and such would be no problem to come by. They can be upgraded to the point where they will easily outrun even the fastest imports (Ferrari, etc), but that would take a ton of work and wouldn’t be a realized dream for a minimum of a decade.

Another thought of mine has been this. A used Dodge Viper (from the mid 90’s to the early 2000’s) would really only cost in the $30k range (the Supra would cost between 20–30k). There are a lot of Vipers out there with less than 50,000 miles in pretty good condition, ready to be sold for that price range. The catch to a viper, is that you can’t really do a whole lot to upgrade it. There aren’t a ton of upgrades done to the cars because as it was put to me “it’s already a Viper.” The only way I could make it faster than the maximum incarnate of the Supra, would be to do MAJOR re-manufacturing on the engine block and attaching a very costly custom built twin turbo charger to it. The cost would very easily get me into the hundreds of thousands of dollars and seems incredibly unlikely that I will ever have that kind of money to dump into a hobby.

Given the choices which would you rather do. Keeping fully in mind that this is entirely hypothetical, as until my student loans are gone neither car is plausible. Would you take the slower out of the box Supra, that would require a lot of work but could become a lot faster, or would you take the fast out of the box Viper, that lacks the upgradeability?