Quite a few champs have an execute ultimate. All of which serve the same purpose, finishing off enemies. But who has the most satisfying execute ultimate.
Edit; sorry for forgetting about not adding the unforgettable, memorable, most popular champ in the game, 
it depends on your perspective and meaning of "satisfying".
In terms of visceral feel? Urgot.
In terms of "fuck yea", Garen (DEMACIA BITCH)
But, there's another way of looking at it.
I'm sure Evelynn finds it very satisfying indeed [slayer-jinx-wink]
this is by far urgot... if you are ever tilted and land his ult you are no longer tilted
I'm surprised there aren't more votes for veigar. Too see your enemy's health bar drop from 60 or 70 to 0 instantly, followed by a burst of maniacal laughter, easily is the most satisfying execute.
Personally I find killing people while shouting “JUSTICE” extremely satisfying.
. You get a big shit eating grin on your face once you know its gonna kill them.
Rek'Sai... Gone but not forgoten...
Her's is maybe the least satisfying but it's still a execute. Jhin's and Jinx's aren't executes. But yeah...
Urgot's is the most satisfying in theory, but in game it just feels kind of unceremonious. It feels like its missing something... almost as if once the chains hit, it should pause for a second, and Urgot should scream "GET OVER HERE" before yanking them to him in one powerful motion... (Scorpion Urgot skin when)
Aside from Urgot, Eve's is the best. It's large, exaggerated AoE effect, and the way it instantly ends the fight by taking her out makes it feel a lot more "final" than something like Darius or Garen.
I say Garen because my screen makes me have an eyegasm.
Obviously 
where you execute yourself by paying 20% of your current HP. if done right before the burst is basically an auto execute
Depends on your side. If you're being ulted, Urgot, since it's so terrifying at first.
But if you're the one ulting, Garen by far. That shockwave it sends across the screen. *w*
There is no better feeling than pulling an enemy into the meatgrinder while maniacally laughing.
Second best:
Rocket snipes across the entire map are so good.
What no karthus?
As much as I love Jhin, Urgot has to have the coolest execute in the game by far. It just looks cool as hell and is actually scary when it's happening to you.
How was Kog'Maw put up there but not Zed... That pop is fantastic.
veigar, do you know how big it can get?
urgot with jhin in close second.
It's not technically an execute, but a few of the ults you mentioned aren't technically executes either, and it's pretty satisfying to kill someone with panth ult.
Urgot is the most execute-y one that truely executes, in contrast with many of the others that only execute in the sense of scaling with missing health amongst those you list though.
Urgot's ult is cool yes, but nothing screams satisfaction more that to see a GIGANTIC SWORD MADE OF JUSTICE LIGHT smite them villains to oblivion.
It had to be Urgot.
and 
are satisfying but after like the 3rd time using it in 5 seconds. It loses a little bit of satisfaction. But URGOT is sexy the whole time.
Now if Darius' didnt reset but was even more terrifying of an execute, or we were talking about JUST Jhins 4th bullet ult. Then I mightve voted them.
There just something so satisfying yet creepy watching Urgots chains drag your opponent into a burning furnace with saw blades. The fact that it terrifies all nearby champions is a really good effect to have on that ult as well. I don't think any other champ in the game has any execute as brutal as that.
RIP ap kog ;(
is the correct answer
Urgots shits on every single other champion here.
This is super difficult to pick. Darius, Garen, Urgot, Evelynn and Veigar easily have the best ones in the game but it's so hard to pick. If I had to pick one though, I'd probably go with Veigar I think. His ultimate is just such a blast :D
