After looking through some back stats, Palmer's done decently well even in losses. Ben didn't put up enormous points last week even in a blowout win with 2 TDs. I'd go with Palmer.
That being said, Mendenhall, even with a good matchup, hasn't run very well. His two best recent games were both against the Bengals, and only because he scored TDs. He hasn't broken 100 yards since Week 6. I really feel the Steelers will end up throwing more, though not to the clip that Ben will end up with great numbers. I see it as a repeat of last week, basically.
Since it's PPR, I'd suggest Spiller. The others just aren't great matchups.viewtopic.php?t=510269