Both are nice but, I would focus on Asheville or better yet the Sylva/Franklin area. There are some great routes in this area and, the Parkway between Waterrock and Richland is probably the most scenic of its entire length. And then you have many other mountainous and valley routes that are near ideal for cycling. The Tour de Cashiers event is on the 30th of April and, its a defining mountain event. But to answer your question, my pick would be Asheville as it offers all venues of cycling routes as well as things to do and see outside cycling. Its a big city. Too big actually.