GW is my choice for black. It's by far the smoothest and most reliable black spray I've found (though technically not "primer", I haven't had any problems with it rubbing off any more than any other spray). Yeah it's expensive, very expensive. To me though it's worth the extra money just knowing that I don't have to worry about the can going bad and ruining the figure. If I'm spending several hours cleaning and prepping a miniature it doesn't make much sense to me to spray any old junk on it
The new GW white is pretty smooth too, though I'll admit that since I primarily undercoat with black I'm not too familiar with many white sprays out there.
-Matt