I'm sure you'll get many answers over on hybridphoto, the general concensus seems to be go for a dedicated film scanner if you have the cash, or if not, and you want to scan 5x4 as well, then the better flat-beds are ok. The best archive is actually your film, it will generally outlast any digital storage medium, and is cheaper in the long run to archive. I have an Epson V700 that I use to scan 6x7 slide and negative and I'm very happy with it. It's not as good as a dedicated scanner, or a professional scanner, but it does what I want and it's very good. You have to ask yourself why you want to scan and what you'll do with the files afterwards.