I don't think that Cangel takes anything from Bangel or vice versa. I think both of them were vitally important to the building of Angel's humanity and heart.
I believe Angel and Buffy loved each other, and always cared even after things ended. I think being with Buffy was the first time Angel ever felt loved -- that, not sex is why he lost his soul. I don't believe that you ever forget that kind of love... but i believe that the loss of the soul broke them irredeemably. There was too much bloody water under the bridge, and no easy solution for the soul.
I believe that Angel and Cordelia built something good out of being part of the same fight -- and it made both of them stronger. Cordelia made Angel find his sense of humor and she called him on things instead of giving in. He toughened her up and helped her let go of the spoiled rich girl BS.
I personally prefer Cangel, because it seems happier and a more adult, more equal relationship. Angel didn't get to make all the decisions or have all the power over little Buffy, even though Buffy probably could have broken him in half. As fragile as she was, Cordelia probably would have kicked him in the teeth if he'd pissed her off.
Emotionally, with Buffy, he called all the shots, played all the head games and had most of the power. Initially it seems sweet to me that he's basically courting her, but as time went on, it felt very paternalistic. He came, he dropped wisdom, he vanished. After he came back, he decided when it ended. He left. When he feared he couldn't protect her as a human, he decided to take back their perfect day and lied to her about that.
Because Cordelia was more confident and frankly, more of a bitch, Angel didn't pull the same stuff with her until season 4 when she came back and did not remember who she was (and may not have been who she had been). That was when he lied to her, and she ended up not trusting him and running off with Connor.
Whenever Angel decided for others -- not just for partners, bad things tended to happen. You tell people the truth, you give them the options. You don't decide for people you love or respect. You don't lie to them. You don't substitute your will and 'wisdom' for their right to AGENCY and choice. I love Angel, but that was a major issue of his, (he did it to Connor too) and Buffy was too inexperienced at relationships to call him on it.
Buffy later in the series might have been ready to deal with who he was and they might have built something, but younger Buffy was more romantic, and less able to put away the rose colored glasses... until Angel lost his soul and stomped on them good and proper.
For the ACTUAL relationship Buffy and Angel did have, it didn't have a chance to mature into something equal and mutually supportive that could have lasted for the long term. Buffy instead learned a lot of those things about relationships from the strong friendship she developed with Spike in BtVS season 7.
I would have liked to see how things might have gone with Angel and Cordelia, with him figuring out how to earn his permanent soul. What if they'd figured out that Jasmine was trying to birth herself and instead of what happened, they were able to save Cordelia, and make his soul permanent (maybe as a gift from the Powers that be for saving the world from Jasmine?) then greatly strengthened, spend season 5 taking Wolfram and Hart apart -- now that would have been interesting TV!