I live in FL so I am partial, we have a great state series going for offroad 250+ entries usually every race, as well as some great companies. JConcepts is a 15 minute drive from me =). Our state series also sees some top notch drivers, Ryan Eckert, Billy Easton, JR Mitch, Gene Hickerson, just to name a few. Loads of permanent offroad tracks, and decent weather year round. But I am a socal kid born, would love to get out that way and check the scene out over on that side of the us.
Just like any other hobby though, the best areas are gonna be the southern states across the map, those states that have great weather year round. Texas, FL, and CA are the 3 best states for ANY hobby period.