I am of the opinion there are a few pests that are super problematic, and a few that are just non-ideal, and a few that people seem to think are pests that I actively encourage.
Bad pests:
Spiders, most crabs, mantis, AEFW, acro bugs, most nudis, fireworms, bobbit worms, isopods, whelks, pyramid snails.
Non-ideal:
Aipstasia, Majano's, normal boring flatworms, vermetid snails, asterena starfish
Good "pests":
Sponges, fanworms, bristleworms, spaghetti worms, all non-iso "pods", almost all worms, any scavenger really, micro brittlestars.