For me its 2-H greatsword decapitation, 2-H greatsword impale from behind a fleeing enemy and throatslit /w dagger.

What execution moves do you find the most enjoyable to watch?

2h sword decap, or dual wield 1h decap, Jedi style.

2h battleaxe decapitation, battleaxe neck-breaker, 1h sword through the chin and out the top of the head. Brutal.

Battleaxe decapitation, where your character knocks them over with the handle and cuts their head off right after. I once did that unintentionally to Grelod, was entertaining to see a big bad orc put all of that effort into taking out an old lady.

1h war axe killcam where the player grabs a wolf by the neck and gives it a mighty hit. It's funny if the hand that grabs the wolf has a spell in it
also the killcam for using Sparks + Flames.

Decapitation all the way. Specially if the enemy is a hard one.

1 dagger throat kill looks cool and it triggers often.