Can't decide who to start for my flex spot, please help!?

You should not start either of the receivers. Ricky is starting to get more goalline touches and has been more effective than ronnie in recent games. Against tbay, i think he's a great start. Benson has had a good year but I can't see that continuing. He has been SO bad before and with mendenhall running so well against him Steelers could have lots of TOP which would lessen his touches.