What's the use of this thread without a poll?
For me the better game is Deus Ex, and it isn't really even close, even though I of course like Bloodlines very much too.
The level design in DX is superior and consistently great, whereas Bloodlines teases you with some nice (although generally very small) levels early on and then never expands upon that, becoming something of a continuous downward spiral with the occasional highlight here and there. DX does lose a bit of its steam towards the end too, but it doesn't have any severe slumps, and the quality remains high all the way to the end. The better level design with more interactivity and freedom also lends for better gameplay, as even though Bloodlines does have many individual levels that are very atmospheric and memorable, it's a shame how linear and limited many of them are.
As far as the settings go, I'll come out and say it: WoD is stupid. Also, maybe I'm alone in this, but a gothic nightclub in Los Angeles would be the very last place on earth that I'd put a vampire into, unless you want to do comedy or parody. Vampires are horrific beings from European folklore, and probably the most effective way of killing everything that is interesting about them is to turn them into goth losers and LA hipsters. It's just an utterly retarded idea from the start, and Bloodlines deserves some credit for actually making it work. I still prefer DX, which similarly manages to weave tons of ridiculous stuff into its setting while still managing to play it straight.
The writing is good in both games, although Bloodlines probably has a bit of an edge because of its superior voice-acting and facial animations, both of which are some of the best I've seen in any game. Music-wise I think Deus Ex is superior of the two, although Bloodlines does have some decent city tracks.
In the end both games are fucking great, of course, but I always felt Bloodlines could've been so much better if the level design had even a tiny bit more Deus Ex in it.