Avoriaz is the gateway to the rest of the Portes du Soleil. There are 3 main ways to get there:

1. Up the Chavannes Chair then the Folliets Chair, then take any of the slopes going all the way down into Morzine village (blues and reds). Take the petit train or walk across the village (5 min's walk) then up the Super Morzine.

Good: Least time off the slopes.
Bad: the skiing above Supermorzine lift is pretty flat until you hit Avoriaz village, so not a great idea on fresh/sticky snow or a snowboard.

2. Ski down into Morzine, walk one block into town and you will see the large bus stop. Take bus A to Prodains (free, every 10 to 15 min's, bus ride is 10 min's) then take the big cable car up.

Good: Takes you straight into the heart of the good skiing.
Bad: Sitting on a bus!

3. Drive to Ardent then take the bubble up from there. This puts you in Les Linderets valley, which is in the Avoriaz ski area and the valley in between Avoriaz and the rest of the Portes du Soleil.

Good: this is the best way to access the further reaches of the Portes du Soleil, as generally if you ski all the way from Les Gets then you have to turn around to get home again before you've reached the other side of the ski area.
Bad: Bus services between Ardent and Les Gets are not great, so you need a car, or Ski Transfers offer a shuttle bus direct to the door of your chalet, definitely worth considering for the big days out on the Swiss side!