And in IWRY, Angel hates the back aches and human physical weakness and all that. He didn't enjoy being human, only enjoyed the Buffy part.
Just want to point out that the backaches & physical weakness is not why he gave up the opportunity to remain human in IWRY.
Angel simply didn't blow off opportunities to become human. The Oracles told Angel that a specific battle was coming that Buffy would fight for him that she would not survive (in IWRY). This was arguably The Scourge.
Hmm, interesting theory. Why do you think the Oracles were specifically referring to the Scourge, I never surmised that before.
I think we can both agree, then, that Spike is a competitor for the title as he can fit the criteria. We just disagree on who wants it (more).
However, I do wanna ask people a question or two. Four: What does Angel loose if he does not get Shanshu? What does he gain if he does? What does Spike loose if he does not get the Shanshu? What does he gain if he does?
As far as Angel, I agree with what Kean says. I also don't discount his desire for love. He experienced love for the first time with Buffy, but we all know where the physical manifestation of that led. No, I don't think he wants to be human simply so that he can have sex, but I'm sure a part of him wants to be able to give himself & be accepted fully by a woman he loves in that way. Wesley said that 99% of the time that wouldn't happen, but why should he take that chance? Sure, he sleeps with Nina, but we all know that isn't true love (at least at that point in time). As a cursed, souled vampire, I'm not sure he can ever allow his heart to fully love. In short, I think there are a variety of reasons he wants to Shanshu.
I am really unsure whether Spike wants it. I don't think he ever even considered the possibility of becoming human again before landing at W&H with Angel. But I don't agree that Spike doesn't care about atonement/redemption. I think he cares more than he lets on. He just doesn't express it, it's not his way. The Spangel moment at the end of Damage reveals to us that in a lot of ways, life was really, really unfair to both of them. They were both young, and had kinda crappy, unfulfilled lives at that point. They were killed & sired and turned into monsters who had little control over their actions (hunt, kill, feed). It's a short scene, but incredibly poignant (of course I think there are other ATS s5 examples of Spike's thoughts/feelings about his actions, and atonement):
SPIKE
Come to tap-dance on the patient, have we, doc? I'd give you the finger, but apparently I won't have the motor skills till the drugs wear off.
ANGEL: A lot of pain?
SPIKE: More than I'd like. But not as much as you would. Just what I deserve.
ANGEL: I didn't say that.
SPIKE: No. I did. The lass thought I killed her family. And I'm supposed to what, complain 'cause hers wasn't one of the hundreds of families I did kill? I'm not sayin' you're right... 'cause, uh... I'm physically incapable of saying that. But, uh... for a demon... I never did think that much about the nature of evil. No. Just threw myself in. Thought it was a party. I liked the rush. I liked the crunch. Never did look back at the victims.
ANGEL: I couldn't take my eyes off them. I was only in it for the evil. It was everything to me. It was art. The destruction of a human being. I would've considered Dana a masterpiece.
SPIKE: What happens to her?
ANGEL: I don't know. Um, Andrew and the slayers took her. Didn't trust us to help her.
SPIKE: Andrew double-crossed us? That's a good move. Hope for the little ponce yet. Though the tingling in my forearms tells me she's too far gone to help. She's...one of us now. She's a monster.
ANGEL: She's an innocent victim.
SPIKE: So were we.. once upon a time.
ANGEL: Once upon a time.