On the one hand, I like the flavor of wizards as a class, I'm sure many other people do too, and they're a D&D classic. So for that matter, I'd also want a divine preparation caster left in place for cleric legacy players.
But on the other, I find that most people play "wizards" (in 2e as well as 3) as psuedo-sorcerers, and find the sorcerous magic system to be easier in play as well as more flavorful than the generic wizard, and as such, the "default" caster in 4e should be a limited-list spontaneous caster. Vancian magic should be held as an option 'till at least 6-7 ed, but should be slowly moved to the sidelines as time goes by.