I've been reading this post with some interest, given that I ride one of the old Brujas. I'd agree with most of the comments, even those with divergent conclusions about which bike to buy. I'd say you won't really go wrong with either, but there is a significant difference in the build quality of the two. Also, the two companies' customer service, as others have mentioned, can't even be compared. I love the Bruja because the stiffness of the frame is on par with a full-on DH bike, and it's not all that heavy at nine pounds (w/ coil shock). The Bruja even puts other Ventanas to shame in the stiffness department (the stellar rear triangle is not the least bit outdated, and it's too bad that it's vanished from the Ventana lineup).
WaState's comments about the head-tube angle and shock-choice limitations are worth consideration, though. You could, for example, build the bike up to be reasonably light, but using a relatively short travel "trail" fork makes the bike unreasonably steep for the frame's intended use/speed. If you think you'd prefer a five-inch fork, I'd advise steering clear of the Bruja. Mine handles perfectly for me with a 170mm Marzocchi 66, but it's still not super slack, as many other FR bikes are. Also, the Vanilla RC isn't great, though it can be magicified by Push. There are a couple of other shock options if you decide you need something else, though they'd likely be spendy (Pushed DHX w/o cap, Avalanche Chubie, Romic (fit my 17" Bruja with a 400 spring), or maybe even an air shock. Granted Ventana has moved on from this frame (though not with the rear end!), but you might also wonder how long the current iteration of the Slayer will last.