I have the same dilemma in a PPR league. Williams has a better chance of scoring but I think Amendola will get more targets. In your case I'd go Williams.
QB: Phillip Rivers, Mark Sanchez
RB: Arian Foster, Ben Tate, Schonn Greene, LT, Pierre Thomas, Thomas Jones, Jonathon Stewart, Michael Bush
WR: Mike Williams (TB), Kenny Britt, Dez Bryant, Santana Moss, Jordy Nelson
TE: Kellen Winslow