During my trip on Vancouver Island I've ridden in: Duncan, Nanaimo, Cumberland and Campbell River. Cumberland had in my opinion the best trail network. The trails were in perfect condition, because of the BC Bike Race that took place one or two weeks before. The trails are perfectly to ride in one go from top to bottom, even when you are unfamiliar with the trails. But it's worth to ask for trail advice at the Dodge City Cycles bike shop, because they can tell you which trails fit to your level of riding.