I have Foster and Spiller ranked very close actually, both around the 17-20 range....but i can see Foster having a larger year than his draft position. Spiller i think has far more upside, and is the obviously superior talent...but plays in Bufallo. It's a tough call, but in a keeper i think i would go Spiller first....Foster has been in this position before and hasnt come through....yes he plays in a high powered offense, but they are a pass HEAVY offense, centred on Schaub, AJ, Daniels, and this year i see Jacody Jones busting out as well. Bufally will need Spiller to be the centerpiece of the offense...(he will lose carries yes to Jackson and maybe Lynch, but they will try to get the ball into Spillers hands in any way possible.) For the upside alone, i would side with Spiller, barely, but would not fault you for going the other way.
As for your handcuff, if you could only chose 1, again i go with upside. Bernard Scott is explosive, and with Bensons checkered injury history, could be the guy in Cinci before long. He is also much younger, and if Benson doesnt re sign in Cinci, Scott is next in line.