The 20-year-old was selected by a media panel following his impressive performances in the month of December, which gained him a place in the England training squad.
"Billy Vunipola is a big mover in more ways than one. The Wasps number eight is a young lad whose error count last season was too high and his fitness not good enough," said Aviva ambassador Will Greenwood.
"Now he looks like a man, and a big, big one at that. He is an outstanding ball carrier, and he has great hands. His discipline has improved enormously and he has remained very explosive, in a good way. He is not super fit yet, but looking like someone you would consider at international level which has been rewarded by the Saxons berth.
"The number eight slot is not nailed down for England despite Ben Morgan putting in a strong game against New Zealand. Billy is still in this and with performances like he put in December will only ensure he steps closer to England – and even a berth on the Lions."
Vunipola has made 18 appearances for the Wasps this season.