I'm leaning more towards Big Show because of his overall history in the WWE. He's been around since the Attitude Era and has been up against the McMahons, Triple H and Randy Orton at various times throughout his WWE career. Big Show also has a good deal of history against The Shield, as Show has been a pretty frequent target of theirs in various beatdowns and six man tag matches in the past.
What I see happening is that Big Show will go down first to help Bryan and will rally against The Shield for a bit. Once The Shield starts to get the better of Show, possibly due to Orton giving them a hand, I see Mark Henry going down to give Show a hand since they're both said to be going after The Shield and the tag titles. After this, I see possibly Ziggler & Miz coming down. Show, Ziggler & Miz are the three that Renee Young talked to last night just before Bryan's gauntlet match, so I'd say Bryan's allies will be made up of Show, Henry, Ziggler & possibly Miz by the time it's all said and done. I think it'll come about next week, resulting in a big 8 or 10 man tag team match for the go home Raw before NOC.