Ok here's my opinion.

DBU, looks a little more grainy when sprayed but dries quick and is easier to fix things as dirt, bugs etc. as it is chemically hardened, seems to stick to primer/sealer better than DBC also, so that is nice for 2 tones

DBC sprays out nice and smooth, good for having less orange peel when done, i've never personally like DBC much at all as it seems to be gummy when you try to sand it unless you let it sit for 1/2hr or more, and have to wait longer to tape on for graphics.

BC is what I use and prefer by far, although it is more expensive, sprays like DBC, but i think it dries out nicer, has better color match, the pearls are liquid instead of powder, sands better than DBC if you have to sand for some reason, if you paint long enough something is bound to happen sooner or later. Plus if your doing 2 tone or graphics it seems to tape much better also. unless you want to wait a long time to tape. it also seems to stick much better than DBC which is important down the road also..

but they are all good systems you just have to learn to work with the one your going to be using, i've used DBU for yrs, then when i went to buy a system i was spraying DBC, just had to many things i didn't like to buy a system, well they had me try the new BC and i was sold on it right away.

hope this helps ya... good luck