Overall? Lampley. I feel that HBO just offers better production value in general and that likely plays into my decision (I'm sure others feel the same). Bernstein does have better insight and is less partial to fighters than Lampley, but I also feel as a boxing fan I have my own insight to what is going on in the fight. So it comes down to entertainment value and I think that's where Lampley has the edge.
Bernstein seems like a legimitately nice guy -- someone who loves the sport and never takes himself too seriously. (I think Lampley's predecessor, Barry Tompkins is similar in this regard). I tended to think Lampley was a little more about Lampley. If I want an audio clip -- it's Lampley all the way. I don't remeber specific Bernstein calls, but there are Lampley ones that I could recite from memory.