The bluegears card uses the latest C-Media chip, like a few others. Not a bad chip, but many long term owners of bluegear cards have reported the cards simply die. Seems they use or were using poor quality capacitors. They could have changed it, but I have not seen anything to either confirm or deny that. That would be my only concern with them.
As far as Xonar goes, you always have to figure there will be growing pains whenever a company jumps into a new business. The XP support seems to be pretty solid at the moment and the early issues they had with the cards have been resolved as well. Not too worried about CPU overhead as the overhead is still lower than my Audigy 2 ZS card.
Seems to be a crap shoot, but the Xonar cards do have better sound quality than the C-Media based cards, at the moment.