Regardless of the merits of one vs. the other, my experience has been that my Hayes-9's have been maintenance free for 6 years and nearly 5,000 miles (with the exception of one pad change). The same can't be said of my Avid Single Digit 7's, various cantilever brakes, or any other rim brake I have. My Hayes-9's stop better in all conditions and require less maintenance/adjustment.

The only mechanical discs I have tried are the Avid BB5's. They weren't nearly as good as my Tektro V-brakes. On the other hand, I also have Avid Juicy 7's and they are significantly better than the V-brakes. The only downside to the Juicy's is that they seem to need to be bled if you store the bike upside down or vertically hanging on a wall.

On one bike I have Hayes Stoker Trail hydro discs. They are very close to being as good as the Hayes 9s, though the 9s feel better to me. Both stop equally well, and both are noticeably better than the BB5s or V brakes. When bled properly, the Juicy's are about the same (IMHO) as the Stoker's, though not as good as the Hayes 9s.

The only rim brakes I have that even come close to the Hayes are the Magura hyro rim brakes with tar treatment on the rim surface (on my Team GT trials bike). They're almost as good, though not quite. Besides, I don't think tar treatment would be good for any kind of riding except trials.

Bottom line: if your bike can support disc brakes, skip the rim brakes and BB7s and get the Hayes 9s. Of all the brakes I've had, they have been and continue to be the best.

Also, I have ridden in virtually any condition (snow, ice, freezing rain, rain, slick sticky mud, sloppy drippy mud) and have never had a problem with the Hayes 9s or Hayes Stokers clogging up. They stop very well, whether wet, dry, hot, cold, muddy, or dusty. The same can't be said of rim brakes.