I don't know why, but lately whenever i read the prologue it feels to me like it's Mercutio speaking.

Logically, it wouldn't be any actual character from the play (especially one who doesn't live to see the end of it), but something about Mercutio's position in the story, the way he knows both sides, and both cares about and judges everyone around him, makes it feel like his spirit inhabits the prologue.

On a slightly related note, we did a production of Henry V a few years ago where the choruses were divided among the whole cast, who came out in base costumes at the start of the play, did the chorus (which basically says "hi, we're actors, this is a stage, please use your imaginations") then immediately got into costume on stage and began the first scene.