Using a 6th level slot, Hold Monster threatens 2 foes.
Hold Monster has a 90' range; Ottos is 30'. 30' is really, really close.
Hold Monster works on foes immune to charm, Ottos does not. Charm immunity far more common than paralyzed immunity.
A foe with legendary resists will not let it be held, unless it it going immediately after your turn. So at best it eats a legendary resist on a boss-type monster.
The effect of Hold Monster is more powerful than Otto's; Hold Monster grants auto-crits on adjacent attackers.
If your save DC is high enough that the monster has a < 50% chance of saving (also rare on big bad beefy bad guys), and there are 2 or more of them, and they don't have legendary resists, and you don't care which you are going to hold -- then Hold Monster is better than Ottos.
Ottos is a spell that shuts down one foe hard, regardless of legendary resists or creature size. There are few spells that match its effectiveness that way. It is a "suck" spell, there is no save.
Hold monster is a multi-target "save or suck", with a recovery save each round. There are plenty of those. Its suck is very strong.