I'd get the med one; easier to acclimate, yet past the "baby" stage.Just something for future reference; I don't know of many fish that grow faster than a healthy volitan. He'll be 10" or so before you know it and will be able to eat fish and inverts. much larger than most folks realize. I've always kept a volitan or two since i got into the hobby and I think the list of what "can't" would be shorter than the "Can' list. IMO, fish NOT to keep with a volitan would include any fish they can eat (obviously); any trigger ( I know its done often, but sooner or later the lions fins are irresistible, see Fenners book). Also, most puffers and any other fish known to be a fin nipper. Lions, IMO, are not aggressive and will not bother anything they can't swallow, I think they are the victims of aggression more often than the instigators. I now have two, in the same tank. I've successfully kept them with with tuskfish and other larger wrasse (great, IMO), large angels, tangs,other larger wrasse, maroon clown ( a big female is a great tankmate), butterflies, and others. Great fish, IMO.