I thought that you couldn't use the GC controller on certain VC games.
I would say get both. I never use the GC controller when I play VC games because it feels so forgein, especially while playing Super Mario World. The Classic Controller is much better for VC games and you said you want to play GC games in the future and obviously you can only use the GC controller with those. I have a Classic Controller and 2 GC controllers. It just works better. I've played on every controller since the NES and the Classic Controller is definatly worth it.