Of the 3 headliners I would go and see Billie just for curiosites sake, as I would like to see how she handles the stage/occasion. I like some of her songs, but it's not what I would call 'festival music' - but I think it's pretty incredible she is only 20 and headlining on the Friday.
Good luck to her.
Paul - 0 interest.
Kendrick - I love rap music, but i don't like a lot of his experimental stuff, so I could take it or leave him.