I try to go to as many as I can, just because I want to show support and make certain they continue here in Virginia. I can't speak to the Hampton Roads or Roanoke areas.
For size, Richmond or Chantilly. Chantilly for the number of dealers and the dealer-junk ratio. Once you realize the front third is for war curios and the back two thirds is dealers and gear, you're good to go and can apportion your time well.
Richmond is slightly smaller, but still has a varied selection.
The others are significantly smaller. I noted at Harrisonburg there seemed to be the largest percentage of private sellers, and also a larger percentage of long guns.
Dale City often has only two dealers, one of whom (Dark Sun) I won't patronize again, but the other (Trader Jerrys) is one I really enjoy working with. Lots of military gear, jewelry, and other "stuff".