As of right now... with no real answer about which of our three interior lineman FAs might return, my choice at #21 is Fautanu. He ticks the two boxes that I look for: he looks like an eventual starter at LT, and he can play LG in the interim.
I might change my mind depending on which (if any) of our current linemen resign. I'd focus on Hunt and be willing to overpay there in order to get continuity, but I guess we'll see what happens.
If we lose all three, then all bets are off... and I might lean towards Barton.
But for now... today, my selection is Fautanu. He is the best combination of NOW and future.