Shared transfers
You'll be on a bus with passengers arriving at the airport at a similar time to you.
These tend to be cheaper, although you might have to wait a little while before your bus leaves (typically not more than an hour).
If your transfer is a door-to-door service, you may also have to wait for other passengers to be dropped off in resort. On the plus side, you'll get to discover parts of Val d'Isère you didn't know existed.
Private transfers
You or your group travel alone.
With this type of transfer, there's no waiting around. You can leave the airport as soon as you've cleared customs. The down side is that this is a much more expensive way to travel, and private transfers are not always available.