This is actually something I've been having fun daydreaming about. Despite Cu saying that Taylor reminds him of his teacher, I don't think they'd click all that well. Yes, I think the two of them would respect each other but I can't see them "Playing nice with each other" as it were. My best guesses based on current compatibility are all Servants who were, well, my reasoning is kinda obvious: EMIYA, Vlad III, Medusa, and Hassan of the Serenity. I just think all of them could empathize with Taylor's problems of "The road to Hell is paved with good intentions" and feeling like a monster in the end.
But I got to thinking.... Just because I think these Servants have the most in common with her and they would resonate with one another, that doesn't necessarily mean that they would work best together. Especially considering Taylor's trust issues. So maybe the best Servant for her wouldn't be one like her, but one that can help her heal? One that could slip past her walls and actually form a connection with her despite being "expendable" like she was thinking of Cu there at the end. Does anyone have any suggestions that they think would be good fits? Personally, I'm giggling at the thought of Taylor summoning Elizabeth Bathory (any version), Jaguar Man, Astolfo, and Tamamo Cat. Ya know, just overwhelm her with insanity and happiness. Lord knows the poor girl could use more of the latter in her life.