Its hard to pick a player overall when the team looked like a shadow of its former self for a pretty long time mid-season.
Meli has had his deficiencies in defence on a number of occasions, but has also put in a number of excellent performances.
Webb has come a long way after a shaky start & has strung together a number of strong matches, as a playmaker & a defender. Most improved, but not the best overall, IMO.
I think Logan Swann has had his best season & is maybe the most consistent performer of the yr.
Overall, I voted for Sione. He grabbed all the attention for his flamboyant syle of play earlier on in the season, but he doesnt shirk the hard yards either, defends well, has a low error rate, a decent work-rate, can play pretty much any position & still contribute.