For the outcome of the attack, it doesn't matter if the attacker or defender rolls. If you have a contest (both roll) it slows down the game.
I prefer the attacker to always roll the dice, since it's the same mechanic you have for all other attacks and you can easily incorporate crit's on a 20 and such. In addition, when it's my turn, I want to roll the dice and see how it goes instead of having the DM roll saving throws and say: "nah, they all saved". I want to be able to curse my own dice, instead of the DM if my attack goes badly.
I do see some argue that it makes no sense to have attack rolls for fireballs or charm spells. I would argue that no spell attack comes out the same and that the attack roll simulates that. If the magic-user is having a bad day the fireball might be all whimpy, off-target or maybe the he got distracted by the looks of that Succubus.
In conclusion:
I want attack rolls for all offensive spells, but I do see that logically saving throws or opposed rolls makes as much sense in a simulationist view, but I prefer giving the roll to the active character, not the passive one.
Slightly off topic:
I do prefer one attack roll even vs many targets (for fireballs for instance), the 4e way of doing it is just slow. It makes spells more binary/luck based, so it's not to the advantage of the players (since one unlucky battle kills character). I am not so sure this is a good idea though.