Best and Worst ultimate in the game

I figured I might as well throw this out there.

Whose ultimate, in your opinion, is the most powerful? An ultimate that makes you shiver in fear when it's off cooldown (dueled Malzahar, flashed by Galio) and an ultimate that you ignore (please don't say Udyr's Phoenix stance, because obviously not an ultimate)

For me, I'd say the best ultimate is Kalista's or Orianna's. These ultimates, while lukewarm alone, are incredible when synergized with proper support. These two not only apply a devastating tenacity proof CC to the entire enemy team, they also create an ideal position to follow up with other ultimates.

In my opinion, Teemo has the worst ultimate. His mushrooms may sting, but unless you stepped into one with someone nearby, you can just go lifesteal off creeps or whatever. Usually if a shroom spots you, you are immediately warned in a very noticeable way, whereas with actual wards you have no idea. Detonating a Teemo mushroom is an immediate gank abort, stepping past a sight ward invites a countergank (if your jungler is nice).