If you need discs, and you're feeling stingy, the BB7 is tough to beat. The BB5 works well when all is well, but my fiancee has em on her ride, and they make me want to kill squirrels because they aren't as adjustable as bb7s. BB7s cost just a wee bit more than the BB5s, and the extra dial at the caliper is totally worth it, imho. If you're buying bb5s because you can't afford bb7s, then you might need a cheaper hobby than cycling. A good place to cheap out is with fr5 levers versus sd7 or better levers.
I've been told that hydros are awesome, and I'll bet they are, but as an environmentalist/obnoxious treehugger, I worry about the vile fluids contained therein. Shimano and magura use mineral oil, but i understand that they don't work well in the cold, so? But you? Perhaps you don't care about DOT hydro fluid. If that's the case, the juicy7s are more adjustable than the 5s. The juicy3s were supposed to be oem only, built to a thin nickel, but then thay released them to the aftermarket, in response to demand for dirt-cheeep hydros.
I haven't ever used the hayes mx4s, but I sincerely doubt they can outdo bb7s, so that's that. I like V-brakes, but i'll probably do discs on my next build, and i'll either go XT or BB7. Still, if you're stingy or broke, Vbrakes really do work quite nicely, for cheap, with no leaking, bleeding, or honking/squeaking. But, at the end of this long-winded post, all i really feel the NEED to say is this:
Avoid Tektro Ios. They make me sick.