The firmer the roller the better.
A personal roller will generally not go soft as fast as the ones at the gym (which are used more), but you'll still want to get the least giving roller you can stand.
My one gripe with PVC is that it has a tendency to slip out. I'm still looking for a good solution for that. Duct tape tends to wear and leave stickies all over everything. I'm leaning toward some sort of heat-shrink treatment or maybe an adhesive and cloth wrapping of some sort.