I was a bit indifferent to the warlock until I read the essentials hexblade. For the first time I felt that someone had nailed both the pact and sword wielding arcanist side of things. I liked the image, the flavour and the mechanics. I like the combination of sword wielding, pact servants, elder itch blast and minor other magics.
Of the others I loved the theme of a star warlock, but they were hampered by the dual secondary attribute problem. I didn't like the teleporting fey warlocks, and I didn't see the dark(?) warlocks as they were somewhere else. Did I hear that they didn't play nicely with others?
I quite liked the way the 3e warlock worked, although felt it was lacking somewhat in choices that allowed distinguishing between different classes.
Hence my choices.
Cheers