My favorite is Stark because he's Lazy and seems to be indifferent about what happens to the other espada. Also hes just all around cool and his Fraccion Lilinette. (Even if her outfit is a little to revealing)
of course stark! he's the primera exact opposite of my most hated espada that barragan old guy. i mean, he's pretending like he's the greatest or something. go and check your number tattoo first you old fart.
I liked Szayel when he first appeared, but I stopped liking him after he became weak and got his ass kicked in such a shitty manner.
Grimmjow is cool, but he's too generic for me. Plus, his resurrection or whatever was a bit of a let down.
Stark seems pretty badass, but I'd have to see him really fight before I could say that he's my favorite. He's close though.
Ulquiorra's currently my favorite. His resurrection looks nice, and his cold nature (though not original in the slightest) appeals to me. It's a relief to see a character in Bleach who doesn't scream all the time while fighting.
Ulquiorra but Stark and Halibel are notable as well. All 3 are/seem strong, cool and composed witch sets them right square above all those other weirdos and berserker (I'm not full up to date with the manga).
I remember having high hopes about Zommari (prior to learning his number and personality) but he turned out to be yet another freak show.