if it was me i'd go with small fish rather then one or two large tank busters, more variety, cheaper, you can house more, less aggression factor on the most part, constantly active (one large fish is sluggish = no activity)(one small fish sluggish you can watch the others), more interesting interaction with more fish, social habits etc. territories and social hierarchy, easier to deal with if one needs to be seperated for recovery etc., easier to deal with loss if you lose a small fish to disease than a large one (and easier and cheaper to replace)and so on.