Well, lets look at both of them: Spartan Laser is almost strictly anti-vehicle, as far as multiplayer is concerned (in campaign, it can be used against Hunters or Brute Chieftans, and its possible against Elite Generals and Zealots, but they jump around a LOT). It has a long charge time which more or less keeps it in that niche. If you were to try using it against players, you're talking a maximum of 4 kills (5, if you're talking Halo 3) unless some idiots line up perfectly- and hold that alignment during its slow charge sequence. But it kills enemy vehicles much faster and more efficiently than any other weapon in the game- 1 burst and your target is gone. Sleeper Simulant is in almost the same boat, but replace "vehicle" with "boss." Its built as a spike damage weapon on bosses, which are much more resilient than Halo vehicles (3-4 rockets kills a Wraith. 20 rockets barely dents a Walker, and I see no evidence Destiny rockets are somehow weaker). In multiplayer, its a OHK with a shorter charge, which is pretty fair for kill potential (I have yet to even step into TTK Crucible, so IDK how many charges it holds). Honestly, its a toss-up between these two, but I'd go with Spartan Laser. It isn't a God-tier weapon like everyone thinks, but it fills its niche (vehicle killer) much more nicely than the Sleeper Simulant. 1 shot to kill a Warthog and 1 more to kill a Mongoose can net you 5 kills. Sleeper Simulant can be outpaced by guns like Black Spindle. The Simulant does have the advantages of higher ammo capacity and faster charge time, though.