Granted there are a few factors to consider so it's not a straight forward question to answer, but in DAMAGE DEALT, who's Ulti do you think deals the most?

I think with the right Item build, Nunu's is one of the best although it is easy to counter.

k well if AOE's count per hero and we assume we hit every hero...

Nunu hands down.

i think it's 750dmg at max level +3dmg per AP.

Usually late game you end up doing 1500+ per char with an AP build, very strong.

With nunu ap, you run in and ult and see all the people start running.

edit oh and you get partial dmg if you are interupted. The only contender for this might be fiddle but even with more AP it does the same damage.

Boris, when Nunu's ulti is at lv3 he does 900 base + 3x AP

nunu yeap

When playing as Amumu, R is the "Win Team Fight" button.

Kayles ult on a carry. Can kill tanks in seconds.

Malphite, anyone?

aaaaaRRAAAAAWRTGH ROCK SOLID!

Malphite's only does 400+ 1 x AP, though he does prevent them from running away. Tho if you use Nunu's Ice Blast effectively then Nunu does too.

I guess id say veigar's primodeal burst single target. Against a caster of course. i Have hit a Ryze for **** near 2k because of how much ap i had and how much mana he had.

Nunu hands down
just flash into the middle of the other team and watch them die