It is tough question. I think Europe has most tracks to choose, most history, and most of us here are from Europe. Also two tracks that I have modeled is from Europe.
Automobilista has shown that there are many really awesome tracks in South America that deserves to be known more..
USA and Canada certainly has many truly awesome tracks, or used to have. And I think no oval track could ever be considered as a track, it is something else. But some Road-Ovals are very awesome IMO. Also interesting fact first ever race track - Brooklands was roval, and I think it was awesome (but it was in England), and it had a kink actually in one part of oval, which instantly makes it 1000times better than usual NASCAR egg...actually even egg has more exciting silhouette.
Africa and Asia not that much. I think Australia + New Zealand possibly has more awesome tracks than Africa and Asia combined. It is only Japan that really pushes Asia for that matter.