Either can work. Bichirs are fine even solitary. If you like cats, try the doradids particularly the Agamyxis pectifrons. Most plecos might suck the bichir's slime coat. It won't always happen but who knows one day it will try to. Bronchis splendens can work well. They grow to 4 inches whereas corydoras are smaller and are at a risk killing both themselves and the bichir.