Both are really bad compared to the options and damage of the Beastmaster at lvl 5, it's quite sad. Hunter is the weakest option in the whole game from all classes and subclasses I tried (Fighter, Cleric, Barbarian, Warlock, Sorcerer, Wizard, Rogue, Ranger)
That set apart, Horde Breaker is better in theory and Colossus Slayer is better in the current game. As much as I admire Niara for her big knowledge and fantastic ability to explain things, I cannot transfer the comparison in the last post to the (current) game. At level 5, what even minor creature you face as enemy dies after 12 or 18 damage (and that's max damage of the rolls)? Ranger damage is quite low and the Horde Breaker Hunter usually does not kill in one turn. That would not matter much if you could use the feature quite often, but you cannot. The range of Horde Breaker is so low that even in big fights with lots of enemies only seldomly it is usuable because the enemies simply aren't close enough together.
Colossus Slayer is boring but at least you can use it almost every shot (although I read that it proccs only one time a turn, is that new?). As many non-boss creatures need several turns to be killed, it is not only a feature against bosses but utilized in almost all instances. If you can stand the annoying presence of a flying minion (I'm quite irritated by the raven, especially the big one, which is the best pet for a Dex based Ranger and will not play Ranger for this reason), take the feat at character creation to summon an animal friend without a spell slot, then use the little raven. It is highly mobile and it's 1 damage can make Colossus Slayer possible in many cases.
BTW in my opinion Larian has to do something to make the Hunter subclass better. It has no utility, in stark contrast to the (Larian-made) Beastmaster, it only can do damage, and in that it is worse than the Beastmaster.
