I
almost always use black. I use primarily the Foundry three stage paints and the 'A' color of the series does a good job covering the black undercoat, even with red, orange, and yellow. If there are any inconsistencies with the first coat, the second and third highlights normally hide them. The Games Workshop Foundation paints also cover black easily and if I'm using GW for a project, I usually start with those.
Another reason for using the black undercoat is that I favor the high contrast created by leaving black showing between each area (between hand and cuff, belt and tunic, etc).
That being said, I have experimented with Quickshade, starting with a white undercoating, painting flat colors on the areas, and then painting on the shading varnish. The results were not bad at all (and can be seen on this forum at
http://www.leagueofaugsburg.com/fightin ... php?t=1657), but they just don't look like my models so I'm back to the black undercoat.