depends
I grew up in VA and learned to really ride in Harrisonburg, but I've been living in Brevard, NC for about eight years now.
It's a toss up really. I think there's more diverse riding in the AVL area, and Asheville itself has more going on than Harrisonburg in terms of jobs, nightlife and culture...but there's a trade.
The riding in Harrisonburg is raw. Rocky, hard to ride, and hard to get to. If you ride to ride, to learn new moves, push yourself outside the confines of the "podium," then Harrisonburg may be for you. That said, you won't find much "easy" riding there, and the locals, while all cool people...are a tight knit crew. There's one real shop, and everyone knows and likes each other. The riders there also run the forest. They get permits to do re-routes, trail work, and hold events much easier than in AVL. With such a tight knit crew of hardcore riders that built that scene, they just have more going on in that regard.
AVL on the other hand, is a much bigger town with about 13 bike shops in the area. I forget how many there are. That said, there is a lot of clickiness. There are plenty of strong riders....but most everyone is always "training" for some dorky race that involves tons of fire roads, or they're "downhillers" who just skid everywhere. Most people do not spend time trying to ride the hard lines, or push what is rideable because that doesn't help your race results. To put it in a different perspective, AVL and the surrounding area is home to more "scenesters." Get it?
AVL also has a unique problem, Pisgah is a temperate rainforest with hundreds of miles of ecologically sensitive areas. There are a few people in the volunteer organizations who are intent on turning everything into machine cut sidewalks under the guise of "sustainability." That term gets thrown around a lot...and as a result some of best trails in the AVL area are illegal, or have been turned in to sidewalks. These IMBA standards, I believe, will result in a sanitized *****ville where everyone rides hardtail 29ers.
I might sound like I hate WNC, but I still live here. There's more riding within a closer drive than Harrisonburg. The riding in WV is amazing really, but from the Burg it's a while in the car. From the Burg you're in the car no matter where you want to go. In Brevard, I can ride the bike path into Pisgah, and that's pretty amazing. Same thing in AVL, you can be in Bent Creek from town in a 30 min ride from your front door, and from there you can ride all day in and out of Pisgah. In any direction, there is tons of riding from AVL. In the winter (in the unlikely event that it snows) we drop just down the hill and go ride in Upstate SC where there is also a decent amount of riding.
If you're a foodie or a music nerd then AVL is a better bet. Tons of locally owned restaurants, with more and more offering farm to table menus and locally grown/raised options. The scene in AVL is pretty cool, theres more money coming through that town than Harrisonburg. The music scene attracts a pretty diverse line up for a white person mountain town, and ATL and Charlotte are not that far away if you're looking for more progressive music.
Honestly, give it ten years, and Harrisonburg will be another Asheville.