Spell slots for life. It combines great versatility over the long run with focused choices over the short term: A mage can be a blaster one day and a self-buffed fighter the next, particularly in 2e. In various Final Fantasy games, in contrast, every mage class is usually the same (and so you only get one of each, usually). In my current Baldur's Gate 2 playthrough, on the other hand, my Fighter/Mage is buffing themself to become a better fighter while my Cleric/Mage is using her Cleric spells for buffing and her Mage spells for damage-dealing, and I could switch that up at any point. I've never seen that kind of build variety in a game with magic points.