I'd keep it in the original format as extracted from the camera. DV format is an IEC standard, and likely to be readable for quite some time to come. It's a pervasive format (it's use extends into industry, not just the home camcorder market), and thus it's likely to be something that can be extracted many years later.
If really want to convert now (to reduce storage requirements), then I'd say mpeg 4 might be a good choice (with your compression settings turned to 'minimum compression', of course). The reason I say that is that mpeg-4 is a VERY widely adopted standard, again making it likely to be readable for many years into the future.
Another good choice for likely future readability (though not necessarily for video quality or compression) is to store the video as a series of DVDs (playable on a television). The large number of DVDs in existence today makes it likely that DVD reading will be popular for many years into the future.
For absolute maximum future-proofing (while not going so far as to store the original computer and software!), I'd say you should store as many conversions of the video as you can, right along side the original video. This maximizes the chance that one of the formats you've chosen will survive the test of time.
You are also going to have to be careful to keep up with your media and make sure the thing you've store it all on isn't going bad, but you have to do that no matter what the format of the video.