THE ROOK!!
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I like rooks cuz of skewers
Pawns literally determine how much space you have in your position. EVERYONE suddenly is scrambling when they get close to the end of the board. You can make your entire middlegame plan, or get a gist of what you can do and where you attack based around the pawns. You can restrict your opponents plans using them.
They are the life of many openings, especially hyper modern openings. In the KID (kings indian defense) play REVOLVES around using pawn breaks to fight back against the white center, and eventually rip and tear it to shreds.
The knight will frequently find an outpost protected by a pawn.
The activity of a bishop relies on what color squares the pawns are on.
The rook will very frequently sit behind the pawns in an endgame, escorting them to being queens, and a rook cannot infiltrate into an enemy file if there are pawns in the way.
The king is protected by its loyal pawns, and doesn't come out of his fortress until the endgame comes, where they too help the pawns to promotion.
The queen frequently cannot infiltrate into enemy defenses if pawns are blocking the way.
Pawns are the best peices 
(sorry if its long, I just like writing)
NOICE!!
Knight you mean....