As far as "archiving" is concerned, I wouldn't recommend converting them at all. It's like cutting up your paintings into smaller squares so they fit in a box. Or, perhaps a better metaphor is converting your reel to reel recordings to cassette. Sure, they take up less space, but later down the road you are sure to regret it. Unless you take the time to learn all the ins and outs of compression methods, (and I assure you, that's a college coarse in itself!) there are so many ways you can degrade the quality without realizeing it, and losing the fidelity of your media. Imagine finding out that you were to receive your Great, Great, Great Uncle's copy of the U.S. Declaration of Independance, only to find that being a gadget freak, he embraced newer technology and had it converted to moveable type with a smaller font so it would fit on a document he could carry in his pocket!
I copy all my recordings to DVDrom in their original, un-recompressed format and store them away. That way, I've always got the original at hand to convert into any other format I may need later, and I can always be sure that the conversion has the best chance of retaining the original fidelity.
If, on the other hand, you are talking about just having a copy of the original to store for easy retrieval on a hard drive, I would first look at what kind of software or hardware you're going to use to play them, and try to go for a balance between storage density and compatibility. Sometimes if you go with the highest compression, you end up finding that it's incompatible with your portable device or proprietary software, and trying to convert it back leaves you with garbled audio or stuttering video.
And keep in mind, storage space is getting cheaper and cheaper. I did an hour and a half long video a while back that came from a DV recording, complete with title sequences, fades and other effects, but I compressed it to an SD Divx format that looked fine at the time, and saved a lot of space. But if I play it on a newer TV, it looks like garbage, even though the original DV footage looks great. I'm really glad I kept those, but all the work I did was pointless. I had no idea.
So, save every detail, just like Nixon did, at least the rest of us will be glad you did!