Speaker buying is difficult and very dependent on the individual's preferences. I think both speakers are probably pretty comparable. I've heard the Vantage's sibling, the Aeon I, at a friend's house and was pretty impressed. B&W also makes very good speakers, although my personal experience hasn't been as compelling as my ML experience - which could be attributed to a combination of factors (listening to a lower-end B&W speaker on my system and the electronics used with the higher-end B&W's I've heard) unrelated to the actual performance of the 803. Best bet is to try to at least demo both on comparable electronics (neither really cheap or obscenely expensive) using demo material of your choosing.

Actually, my work is quite unrelated to the home theater field. I'm a mechanical engineer, and I design HVAC systems.