In a standard 12 team league should the flex position always be filled with the player with the highest projection for that week (RB, TE, WR) or is there more to it then that?
I think for the most part that's the way to go. A lot of time it's really close so you may have a gut feeling or feel safer about a RB. Some prefer to play as many RBs as possible and may lean that way if the projected points are close.
If it's standard, I lean toward RB if the projected points are close. In PPR I lean towards WR.