1
S Tier
These ults work so well, they basically make sylas a counterpick to these champs.
2
A tier
These ults work especially well with Sylas's kit.
3
B tier
Nothing too special, but they work.
4
c tier
Tricky to use, But can be pulled off.
5
D tier
Little to no synergy with Sylas's kit, CD's are very low, Other ults do the job better for you, or they are just designed entirely around the champion they came with.
6
f tier
Don't Even Bother.
Btw Kayle's Ultimate skill can also be pretty good on him. I play Kayle top/mid a lot (she's my main) and it can be a real pain for our team when he steals my Ultimate.
you can also add Nocturne as well if you want. It's a great engage tool and isn't dependent on other abilities so Sylas can use it pretty well.
I've seen Mordekaiser's ult working well on him in Aram. But I don't know if it generally be always good. Still, it doesn't seem dependent.
btw, I'd like to know what happens if he steals Quinn's Ultimate. Have u tried it? (I personally don't play Sylas.
With this said, stealing an enemy Sylas's ult can indirectly be as overpowered as an S tier pyke ult depending on what the enemy sylas steals as his ultimate.