garden eels are extremely hard to care for, and very delicate, best left in the ocean, even in the case of public aquariums.
ribbon eels are hard to get to eat, and also delicate and large. best left to very experienced keepers.
as for golden dwarf morays, a wondering choice to keep in a 55g, and one of the only eels besides the two previously mentioned that would be able to live comfortably in a tank that size once they reach there adult size.
I would recommend them, they seem (from my prior research) to be small, colorful, and peaceful (as much as an eel could be). they maz out at about 12" and are much less likely to go after shrimp, crabs, small fish, ect then other species.
a cool 55g tank would be a golden dwarf moray eel, a dwarf lionfish, a leaf scorpionfish and 1-2 medium sized open water swimmers.