If Vash gets his Angel Arm... Kid is screwed. Big time.
Without it, I'd say Kid would win easily; especially if it's his recent version.
Angel Arm is actually country level and up...
Also if this is EoS manga Vash he can make fun of Soul Eater as a verse without even being serious.
1. Manga Vash at his strongest wins like it's a joke.
2. Anime Vash with AA and losses without it.
3. Non EoS manga Vash is pretty much a toss-up but giving it to Death because he probably has better DC.