I would go with "Beasley," he is the safety valve and seems to be open on every pass play, and he makes catches others wouldn't. I think we tend to take him for granted.
But, I would agree that Williams has been a great find at RT, hard to argue against him as the "secret" MVP.
While I think Zimmer and Bass are coming along, and both have had their moments (good and no so much), I need to see more consistency over time to put them in this discussion.