Darla before her pregnancy is too cold and transactional for Spike (who is very sentimental and emotion driven) After giving birth... She is dead.
Yeah, I have to agree. The only Darla who might have had a chance of working with Spike is the human one who discovered she was dying. That woman had humanity. Spike's entire existence is defined by emotion, specifically by love and passion. He tried to become what Cecily would have wanted. He became what Drusilla (and Angelus) wanted. He tried to be what he thought Buffy wanted. He is always motivated by the people he loves. He wouldn't be happy with someone like Darla. Say what you want about Drusilla (and it'll probably be true), but she was a passionate person.
I remember talking about this back when the show was still on, and I still hold the same opinion—vampires' personalities seem influenced by the dominant traits of who their hosts were while alive, though definitely twisted to something more evil. Angelus' whimsy and overindulgence is adapted from Liam's party animal nature, Spike's single-minded focus on love is the same as William's, Darla was a prostitute and still "sympathizes" with them (though it leads her to kill them), the Xander and Willow of
The Wish are still inseparable, and so on. And, of course, in
Dopplegangland, Angel confirms this indirectly, when Buffy claims that the personality of a vampire has nothing to do with how they were in life in an attempt to make Willow feel better about her doppleganger.
Angel is manipulative and ruthless.
I don't think I'd describe Angel as manipulative and ruthless, though he is certainly
capable of being both at different times in his life (existence, whatever you want to call it when someone is immortal.) I wouldn't describe him that way, though, because I don't think he
is those things most of the time. It gives an impression of him that I don't think is accurate. Now if we're talking about Angelus, then I would agree that those are appropriate adjectives to use.