For storm footage, I want to be able to store each event in a couple of different places before I'm done, so I save the original tape (I never re-use a tape for storm footage), and if it's important enough to really save, I'll save it again onto a dig 8 tape as well. I also don't want to run the risk of digital artifacting on storm tapes, and treat them like my children. Though I've never had a noticeable problem with it, if you drop your recorder (yes, done it) ... or get it close to a magnetic field or something, you'll mess with the digital signal and get all kinds of craziness.
When doing video for use on the air, I often record over shots multiple times on the same tape and never notice artifact issues during editing. These are typically the standard people walking down the street in the rain or sunshine shots that you see on TWC - and I have to watch closely anyway to make sure there are no digital issues or other 'glitches' (color, focus, composition, etc.) before the video goes in, naturally.
I've never noticed a difference between brands, but usually buy Memorex mini-DV tapes and Digital 8 tapes both.