there is only one choice paul component http://www.paulcomp.com/ the motolites these are the most powerful v brakes out there. Plus they are far easier to get perfectly centered and they ar the smoothest out there. the levers really work well too. butthey cost more then disc brakes. but I found they worked almost as well in the rain too.
I was thinking about the Avid SD Ultimate, but there is a large price difference (as in $75 for just the Ultimate brakes versus $30 for the SD7, and $16 or so for the SD5. Is the premium for the SD Ultimate worth it? If not, the SD7 seems to be at the right price/performance ratio.
Just comparing, XTR brakes are $83, and XT are $45 each. I have not read anything negative or positive about Shimano's V-brakes, so may just go for the Avid because they have a lot of positive recommendations.
I have SD3s and they suck hard. I havent yet gotten them to stop squealing, regardless of toe. The pad distance changes whenever you open the brakes up to take the wheel off. on top of that, they have very little power. the dura ace road brakes (on my roadie) I have are 50000 times better.