What makes a good investment I believe are the coins with "aura". It might come from its sheer rarity, when you see 1934 on a wreath crown there's an aura about it (albeit psychological as it looks exactly like a 1932!). It might come from its sheer beauty-ever seen a well preserved 5 guinea piece in person..it might be fashionable- some time ago it was Russian coins, then Chinese, now Islamic? With English coins its just about any coin type/denomination I guess due to the number of growing english coin collectors.. It might be accessibility.. For example ask can you buy one of these coins in this condition on the Internet tonight? If the answer is yes, I'd say aura is low... And coin condition- obviously important, but coins were made to be circulated, aura is high on an object that defies logic... And to see some details on the design of rate coins can be breathtaking. V high aura...!then historical importance can create incredible aura, with the history encapsulated in a small beautiful round metal manuscript...