I think the big difference is that for the quest cape you have to have a good and balanced personage. Good skills and good combat. For a skill cape u don't have to have trained all skills. For example: if u hate farming, u can easily get a skill cape without farming. But if u want a skill cape, u'll need to have trained all skills, also the ones u hate. Btw I'm aiming for a quest cape too, but got bored at some time, and there are some really though quests left. Well, I'll do them sometimes...