I am not an expert, but I think that BG-42 and S30V should be close, with the nod going to S30V S30V has more vanadium, which makes very hard carbides and thus greater wear resistance. S30V also has the advantage of the CPM process which ensures an even carbide distribution. BG-42 has more moly and also a higher recommended hardness (BG-42 at Rc 61-63, S30V at 57-59). I don't know this for a fact, but it wouldn't suprise me if BG is easier to sharpen due to having less vanadium, so could be better in practice, if not theory.
I am surprised at the lack of interest expressed in this thread for ZDP, friction-forged D2, S90V, etc. It appears that most people are happy with non-exotic steels that are proven, with I think at least one person even naming 1095 as his ultimate steel. For me, I am not. Maybe having used a couple zdp knives has whetted my wish for better & better blade steel.
I also concede STR's point that for a lot of us sharpening gear & ability is a weak link. I use a Spyderco sharpmaker and DMT diamond hones w/ DMT's 'Aligner' (angle guide similar to Lansky guide). Both work reasonably, but I am not really satisfied with either. I guess sharpening will always get short shrift. Nobody ever posts pics of their cool new sharpener, do they?