These 2 are both very fast and in a way they are both assassins. (Killua is a complete assassin, but Sasuke also uses stealth to take on his enemies once in a while) A major difference is that Sasuke has jutsu and the sharingan. With the sharingan he can copy Killua’s moves. Not that he’d need them since he’s much stronger. Killua has some pretty great speed, but I don’t think that it will be enough to defeat Sasuke. Sasuke wins
Fanfic version below
DReager1.com 
Killua will ba the one who’s going to win.
I dunno about that. Sasuke is a formidable opponent and he keeps on getting stronger!
Ok so dreager is right about this one
Sasuke does beat killua
Way stronger, way faster, more abilities and far tougher
The only version of sasuke killua could beat would be kid sasuke
Ya know, the one in the image, that version of sasuke is not as fast or as strong as killua yet
So
Killua wins agiants kid sasuke low diff
Teen and adult sasuke wins agiants killua low diff