In all seriousness, the O-Line. It doesn't matter who you put at QB, if a OL can't block, then a RB can't do much, and a QB can't do much either.
But I think we're going to be pleasantly surprised with our Offensive Line. But I think the OL is the piece that holds it all together. We've had years where we had playmakers, but no O-Line. We had years where we had a good OL but no playmakers. We had years where we had a great offense, but a crappy defense. We had years where we had a great defense, but a crappy offense that went 3 and out every series.
We just need a year where offense clicks and sustains drives and scores. And we need a year where the defense can stop drives and get off the field. We need it all to work in sync. We haven't had that in a LONG time. Ever since 2007, IMO.