Flex help PPR (1 Viewer)

I currently have Peterson as a 3rd RB this week. We start QB, RB RB, WR, WR, Flex, TE, K, DST. 12-team PPR league. pretty standard scoring with bonuses for long TDs.

Peterson
Riddick
Beasley
Moncrief.

Explain your answer, please.

Currently,
QB: Palmer
RB: Gordon
RB: Cook
WR: Brown
WR: Cooks
Flex: Peterson
TE: Fleener
K: Crosby
DST: Seattle.

I don't really believe in Peterson this year but it is a revenge game... While I want Abdullah on my team to get all the looks the game script could cause Riddick to get a lot of looks and its full point PPR. I would go him, but I know plenty of others would go Peterson.

I went Riddick. 

Probably blew it, so far I have Peterson in there, still time to change to Beasley though.