I've heard both these speakers and they are so radically different in design and execution it's funny to see them mentioned in the same sentence.
If you prefer a more laid back sound the Vandys are an unbelievable bargain in the price range. Some feel they sound very natural, while others find them a bit dark in character. I fall in the latter category but respect the overall high level of performance and would recommend highly that you give them a serious listen. Bass is also outstanding for a speaker at this price. One caveat is they are fairly placement sensitive so if you have space restrictions they may not work in your room.
As for the B&Ws, take the inverse of everything I've said about the Vandys(including the value part) and there you have it. I could name ten speakers off the top of my head that sell for the same or much less than the 804s that I'd much rather have(see below for short list). The biggest problem for me is the metal tweeter--the thing just can't get out of the way of the music. Every time a cymbal is struck there is a peaky, sharp character that draws my attention to the tweeter. It's not so bad on classical, but jazz, blues, pop don't work. The midrange is very good if a bit dry relative to others, and the bass is tight and tuneful, but not nearly enough depth/impact at this price point(I think you're paying up big for the cabinet work). Let me add that I've heard these with super high-end electronics and although it obviously helps(as it does with all speakers) the basic limitations still apply. A lot of people love these and they are very high-quality speakers so you should obviously listen for yourself to see if they work for you, but you were asking for our thoughts so there it is.
At this price point I'd strongly suggest you look at Silverline Sonatinas, Soliloquy 6.2 or 6.3, Joseph Audio RM25si, Triangle Ventis, Gershmann RX20, or Audio Physic Tempo III. All of these in my opinion offer much more value and are better in just about every way than the 804s and are more revealing than the 3As if you find the Vandys are too laid back for your taste or don't work for some other reason(looks, size, etc.).
Those are my thoughts for what it's worth, but the bottom line is you really gotta go out and listen for yourself. These speakers are so different you'll know in about a minute which one works best for you. Best of luck.