Sets ?

Well, that is open to difference of opinions. If for investment purposes only than pretty much anything you save now will be worth more than face some day. so sets or key dates will rise in value, but so will your spare pocket change. For resale value sometimes people would love to take the work out of things and buy a completed set with a little bit of an inflated price for having a complete set already put together for them.

From a collector's standpoint sometimes it can be really nice, not to mention give a great sense of accomplishment, to put together full sets and gradually upgrade to nicer coins as time goes by.

Your best bet is to do what gives you the most happiness while you collect.

I've sold 44 complete Buffalo nickel sets (no overdate; no 3 legger) over the last 54 months and my sense is that there is better value to be realized in selling the coins, especially the keys, individually. However, it's a LOT easier and a lot less work to sell a complete set especially if you're selling them on ebay, as I do. So, you sort of have to pick your poison.

Collect sets, sell coins.

If your intent is to use coins as an investment vehicle (you're one of them, eh? ), stick to keys. Their popularity will survive a downswing in collector demand, and they appreciate above their more common peers during periods of increased demand. It's my opinion that key-date coins are one of the most solid long-term investments, if you define long-term as "solid, guaranteed but not hyperactive growth in value."