Personally I would avoid VHS-anything, the image quality really isn't there and the only advantage I can think of is that it plays in a standard VCR (with an adapter, so you still have to carry the adapter tape around).
HI8 isn't bad for the price if you don't think you'll be watching what you tape in 10 years.
The best compromise is probably Digital8 (which basically means you'll be buying Sony) primarily because you can play standard 8mm tapes (8, Hi8,etc) plus you record in digital format on standard inexpensive tapes. Although they do run twice as fast, so they only record half their 'listed' time length.
Other reasons I can see to go with Digital8 is 1-if you need backwards compatibility with any existing 8 format tapes you may have or 2-you want to use it to archive existing VHS material onto the Digital8 media by hooking up your VCR.
The purported advantage is that it records in a digital format on a standard size tape, so the quality shouldn't degrade over time like an analog tape will (8, Hi8, VHS, etc.).
The signal is supposed to be identical to DV if you're using the Digital8 media.
I own a Sony Digital8 TRV310 and am quite happy with it for what I do. The price is pretty reasonable for the unit as well as accessories. You can always find tapes cheap and easily (as opposed to DV or miniDV). This is the primary advantage of Digital8 over DV.
If I had to buy another camera right now, I might be tempted to go with a DV camcorder just because they're so much smaller and lighter, but you should know that the image quality isn't any different, nor is the archive potential of the media. They generally do cost quite a bit more though.
I'm no expert or anything, but I hope this helped.