https://en.wikipedia.org/wiki/Google_Lunar_X_Prize
My bet would actually be on SpaceIL or Astrobotics to win the prize. Astrobotics has been the consistent winner when it comes to demonstrating intermediate goals; they won the prizes for Landing, Mobility, and Imaging, and seem to have a solid engineering effort based out of CMU with partnerships with major U.S. corporations. SpaceIL has some interesting design choices that limit risk, eg. they're launching on a SpaceX Falcon 9 and they aren't building a rover, instead lifting off via rocket and flying to a second destination 500M away.
Moon Express has two major risk factors against it: they're launching on an Electron, which is a rocket that has never successfully flown before and won't be commercially available until 2017, and their founder has a reputation for making grandiose promises and then running away with the money. (He founded InfoSpace during the dot-com boom, sold all of his stock at the peak even while revenues were declining, then was ordered to pay $247M in insider-trading fines by the SEC.)