This depends on how the caster/mechanics division is handled.
IF the PHB says (probably more eloquently): wizards use vancian, sorcerers spell points, warlocks AED and clerics/druids spontaneous; but check with your DM becauce he may use an alternate system (see page XXX in DMG about alternate spellcasting systems) I'd be all for that. Every class is unique and the ability to swap them out is a DM option somewhere in the DMG.
I don't want: Pick your class (wizard, sorcerer, warlock), pick your casting method (Vancian, points, spontaneous or AED, check with your DM which system he allows). I'd like to see internal consistency be assumed, and DMs have to house rule it out if they choose to micromanage that much.
Choosing the default caster method should be on par with rewriting deities to fit your world, not step 7 in the PC creation process.