Sio Moore, Corey Nelson, Martrell Spaight, or Deandre Levy?

Heading into my league's semi-final matchup (it's a 17-week league), I currently have Sean Lee in my LB spot and Tahir Whitehead and Preston Brown in my 2 defensive flex spots. I have Josh Bynes on my bench from when Whitehead got hurt before, but I'm going to drop him and shore up my linebacker corps with another starter or two just in case. Moore, Nelson, Spaight and Levy are among the available players to add, what would you do here? I'm leaning towards Moore just because Deone Buchanan is on IR, whereas Brandon Marshall or Will Compton could still conceivably be back in the next week or two. What do you think?

Also, how worried do you think I should be about Whitehead's snap count with Levy being back? Whitehead still had a nicely productive day even on less snaps than usual, but it's still concerning. Would you even start either one of them this weekend?

I guess what I'm asking is what order would you target the free agents in, and which overall 3 would you start this weekend?

Update: Picked up Moore at FAAB, dropped Bynes. So my current LBs are Lee, Whitehead, P. Brown and Moore. Lee is locked in as a starter, obviously. Having a hard time picking two out of the other three, but I'm leaning towards Brown and Moore, based on snap count alone and the uncertainty surrounding Whitehead/Levy, with my only hang-up being that the last time I benched Whitehead, he blew up.  Anybody have any two cents to chip in?