How about if reality is not a requirement, either?
Batmobile. Either one the fictional ones or one of the various models people have made.
There's also some attraction to the monster car crusher trucks. Cut me off in traffic now, bozo. Or put up curbs in parking lots that try to prevent me from driving directly to the exit.
My favorite car would have some sort of gadget underneath that would rip up speed bumps.
If we want to restrict things to "real" fantasy cars, probably some sort of 1960's classic convertible land barge. Maybe the stereotypical ragtop pink Cadillac. (Despite the fact I'd never want to really own one if cost, reliability, etc. are a concern.)
There's also still a cool factor about a DeLorean, if practicality is not a concern.
Maybe if Jay Leno leaves me all his money, I'll get a fantasy car collection myself. Including customizing a Hello Kitty Testarossa.