I voted for Spike, if there was ever any doubt. 😛 But I also really like Drusilla. I didn't like her the first time I watched the series, but on subsequent rewatches and after I watched AtS, I found her a fascinating character. I love the dynamic between Spike and Dru, too.
I never really liked Darla all that much, and I'm not an Angel fan.
I do think though that there's so much to be explored with the Fanged Four, be it in fanfic or fanart. That said, there's one fic that's pretty much influenced how I see the characters and their journeys, so much so that I've incorporated it into my 'personal canon', lol.
It would have been interesting to see more of them on screen in the shows.