After I had had the game for a fortnight, I was wondering this question over and over again. I couldn't decide which one was worth my million more, and I was even on the fence about wasting money on a premium rather than to keep saving for more standards.
Finally, I borke down and picked up the F1. It wasn't until a month later that I got an enzo to see if I made the right choice.
The answer: hell yes. The F1 is a better car in almost every aspect. Better handling, great sound, very fast, and very fun to drive. Plus it has a very interesting cockpit view, which for me is the final bonus.
Go with the F1, the enzo can wait.