Depends entirely on the opening being played and the game situation. I like to swap queens early and rooks late in the game, and then protect and advance an extra Pawn during the endgame. Then a Knight comes in very handy because of its ability to jump, or a Bishop because of its ability to control diagonals across the board. I also use the King pretty aggressively when advancing the Pawn.
"O people, we created you from the same male and female, and rendered you distinct peoples and tribes, that you may recognize one another. The best among you in the sight of GOD is the most righteous. GOD is Omniscient, Cognizant." (49:13)