It really just depends,
The BBO English Server has a low population, so if you are looking for a populated English Language server, picking the most populated VCO server could be your better option.
If you don't mind playing on a German Language server or a low population English one, then BBO has the advantage of considerably cheaper IM (IM can be had as cheap as $.015 per point VS $.055 per point on VCO) and IM consumption rewards seem to be better in general although they have not been great lately.
I only have in depth knowledge of the BBO servers from an actual game play stand-point, but most of the really nasty bugs that have plagued VCO don't seem to have been available on BBO (Ship Cabin socket bugs, stat bugs, major game-play changing exploits). Not saying that BBO has none, just that the biggies seem to have been avoided. VCO seems to have better support, which is scary because its not that great. But BBO support seems to have improved some lately.