I'll just say, I used to used WheelSmith Spoke Prep, until DT unveiled their ProLock nipples.

Why? I am not a hobbyist, nor a builder willing to fuss over wheels after they're built. Often, I am sending my wheels to other parts of the world, so I will likely never ever see such a wheel again. Because of that, I leave nothing to chance. I use spoke washers where required as well. Bottom line is if you need some substance to keep a poorly built wheel from falling apart, you are doing it wrong. However, if you are using them as a failsafe for a wheel that would be fine without, then use whatever you want. Even though I offer a truing and spoke breakage warranty for the usable life of the rim, I seldom-really seldom ever see a wheel come back for tweaks of any kind. Even slightly flatspotted wheels won't get worse because even if one spoke is detensioned by the dent, it can't unscrew itself further, neither can its neighbors.