The best version of Outrun, as endre said is either the arcade version or the Genesis/Megadrive version. If you have a Sega Saturn, you can get Sega Ages - a game that has Outrun, Afterburner 2, and Space Harrier all in one disc, and is arcade-perfect. That would be the best choice for outrun if you can find the console and the game. Also, Sega remade Outrun on the Xbox, and it's titled "Outrun 2." The tracks are redone using real instruments, and the sound flavor of the originals is well-preserved. You can try that too.
The PC Engine/TG-16 version is quite nice too, for an 8-bit version anyway.
I think the C64 version was pretty bad actually. No forks in the road and the music was not very authentic. Turbo Outrun got a much better conversion.
And you're is absolutely right about Outrun 2, it has a great soundtrack with respectfully done arrangements, plus a few new tracks that aren't bad either!