in the first three seasons prue seems to be the most powerful and main sister same as buffy is he main scooby,
they're both the most powerful, they both date bad ass men who they turn good, andy scarifices himseld, spike scarifices himself, they both die, they both look after they're sisters with they're life, they both have issues with their dad, they both are the main fighters and they both have the women empowerment thing going on
there's loads more examples but i don't think i need to ramble on lol

I agree with everything debs just said. The rest of the options I can't see anything in common. Cole seems to have more in common with Spike than Angel, he turned from evil to good to be with the woman he loved, and he also set out to kill her at first. Leo isn't as fatherly to the sisters as Giles is, and more often than not Giles steps back and let's Buffy fight, while Leo fights with them. Piper would probably have more in common with Willow I think than Buffy.

i think paige and early willow would have a similar vibe too but i can't say why

Both are very similar, while Cole was more of a dreamer when it came to love while Angel was more realistic,Buffy & Piper are way different:):):)

i'm going with Cole&Angel, as they both were good then went evil and got sent to hell by their Lovers lol :]

i choose piper she didnt like being a witch and buffy didnt like it either and didnt want to be apart of it from the beginning

Buffy and Prue are most alike.