Mei (I can't think of anything more cold (eheh pun intended) then freezing your opponent until they are completely frost bitten and unable to move... before stabbing them in the head with a sharp piece of ice... at close range ;.;

Symmetra (I have a blast playing as symettra... but can't help but think about how scared players are as they hopeless try to escape from the maniac who slowly zaps them to death)

Roadhog (There is not much to explain here... like the others it is close range, messy but quicker than the two above)

Winston (He has a lot of time to think about who he is electrocuting)

Reinhardt (quick but gory)

Pharah (let's watch the red fireworks mommy)

Junkrat (not much to explain...)

DVA (the last three don't really have an order... I put dva on this list because her eliminations would absolute carnage in real life)

Sombra (rending your opponent almost useless, with no way to escape. before slowly killing them)

Hanzo (ever go up after an elimination and see your arrow though there heads... yeah, that's the must humane he gets)