Stamina for warriors, and Mana for Mages!

or maybe just Stamina for both

Magic users are supposed to be powerful, that is the point. The trade off is that they are weak physically, so they are glass cannons. I prefer a cool down/recharge for spells then to have to drink magic potions or resting. I do not like the idea of magic getting weaker with more use, that is silly and will not be helpful when you are fighting a flood of enemies.

Perhaps two forms of magic: Small invocations for combat, conversation and such that are quickly cast and easy to learn. Ritual magic for healing, divination and the larger spells that requires grimoires, components and all manner of arcane paraphernalia.

 

I think this would be great - the Vancian spell system was so weird when I first encountered it, but it provided a huge amount of tactical depth; that said, a cooldown/mana based system can be a good foil to keep it accessible. I really didn't like the Neverwinter Nights spell setup, where resting was basically instant and had no danger - giving it the worst of both worlds.