It really depends on what position(s) on the O-line Pete and John want to improve the most. If they're not sold on Gilliam/Sowell at LT or Webb at RT there could be a good chance we go OT in the first. After late first/early second there won't be a lot of day 1 starting caliber tackles left so we would have to strike there with our first pick. I think Carroll really likes the LT competition we have going on and looking at the contract Webb got they trust him enough to at least hold the fort down this year. Glow also seems to have won over the coaches and will more than likely start at RG but center and especially LG could use an upgrade.
Point is that taking a center in the first round would be a reach. Even Ryan Kelly. The guard position really depends on what they want there. Do they want a guy who can play guard at first to later take over one of the tackle spots (Think guys like Ifedi, Coleman or maybe Whitehair) or do they want a guy like Glowinski who can really make the LG spot his own (Garnett, Mcgovern or Westerman for example)? If it's the first scenario we're looking at a 1st or trading up in the 2nd but the second, and more likely, scenario could be handled by staying put in the 2nd or even waiting for the 3rd and still get a top class guy.
That said, I think the OL situation can be handled without using a first rounder. Then we look at our next biggest holes: RB - we only have 2 on the roster and our leading back is coming off an injury, DT - interior pass rush is still not addressed and Siliga might not be the stop gap some are expecting as a run stuffer either, SAM - last year's starter left and we haven't brought in anyone new to take over and we're thus left with two back ups going at it.
Which one of the three would I choose? Easy, DT. SAM isn't a position worthy of a first rounder and neither is a 3rd down RB (even a number 1 RB can be gotten after the first round quite easily nowadays). DT on the other hand has plenty strong options available when we pick. I wouldn't be surprised if one of those guys is exactly what we're looking for.