I've kept practically all the commonly sold reef safe hermits and the scarlet hermits (Paguristes cadenati) are definitely the best imo. At least across my tanks and 30+ hermit crabs they steal the least snail shells and seem the most peaceful. Also never had an issue with them damaging corals and some of mine are well over four years old. My Halloween hermit (Ciliopagurus strigatus) is decent too but has ripped some small corals off the rocks and killed every other individual of its own species I've tried adding. I'm not a fan of Clibanarius sp. like blue legs since they seem most boisterous, crawling on corals and killing snails or other hermits for shells. Lastly the Calcinus sp. hermits like electric blues and Hawaiian zebras are decent, though I suspect them of slightly more misbehavior than my scarlets. As for other clean up crew I can say I've had bad experiences with emerald crabs killing small fish, great experiences with tuxedo urchins, and I've never kept a peppermint shrimp. I tend to steer people away from sifting gobies since many species starve unless given an extensive mature sandbed and special accommodations, but I know people do keep them happy and healthy so it isn't impossible. I will also recommend bristle worms still since you'll probably end up with some regardless and they are practically unseen in most tanks. Great detritus control and can clean both in the substrate and the rocks. Maybe try selling her on a fighting conch for the sandbed, it's a snail but they have comically cute eyes that peek out from their shell and a long vacuum cleaner looking snout that most people find endearing.
