Benjamin Olson
Hero
I think you're rarely going to use Hideous Laughter, because it's concentration. You went to the trouble of getting Hex with a feat, and more often than not you won't want to drop your Hex for a single target save or suck that will likely only incapacitate an enemy for 1 round if it succeeds.
I'd go with Sleep. Sure you are not going to have a lot of encounters at level 6 where it is the win button like it frequently is at levels 1-2, but occasionally it still is the win button if the DM decides to just throw 40 goblins at you or something. It also continues to be useful if you need to subdue an already heavily damaged enemy; if you want to incapacitate a mount, familiar, or other strategically important low level enemy; if you need to defeat a low HP enemy who is exceptionally difficult to damage or finish off for some reason, and, to me most importantly, when you need some nonviolent incapacitation of random npcs, be they hapless townsguard or innocent civilians.
I'd also say that going forward Hideous Laughter is more directly superseded by higher level spells, whereas Sleep continues to shine within a niche, albeit one that slowly gets smaller level by level. So if this is just a placeholder until you can replace it with a level 2 spell it might be easier to say goodbye to Hideous Laughter, whereas if you are going to be stuck with it for many levels because you are taking mostly Wizard levels from here on out or something I'd pick Sleep as the one that continues to excell for a handful of niche purposes.
I'd go with Sleep. Sure you are not going to have a lot of encounters at level 6 where it is the win button like it frequently is at levels 1-2, but occasionally it still is the win button if the DM decides to just throw 40 goblins at you or something. It also continues to be useful if you need to subdue an already heavily damaged enemy; if you want to incapacitate a mount, familiar, or other strategically important low level enemy; if you need to defeat a low HP enemy who is exceptionally difficult to damage or finish off for some reason, and, to me most importantly, when you need some nonviolent incapacitation of random npcs, be they hapless townsguard or innocent civilians.
I'd also say that going forward Hideous Laughter is more directly superseded by higher level spells, whereas Sleep continues to shine within a niche, albeit one that slowly gets smaller level by level. So if this is just a placeholder until you can replace it with a level 2 spell it might be easier to say goodbye to Hideous Laughter, whereas if you are going to be stuck with it for many levels because you are taking mostly Wizard levels from here on out or something I'd pick Sleep as the one that continues to excell for a handful of niche purposes.