I ski every year here in Chapelco (www.chapelco.com) in San Martin de los Andes. The skiing in general in SA is mediocre compared to France/Europe and the US, especially the number of runs and service/price ratio, but always better than the Chilean resorts, may of which just have a few basic lifts and few runs, while being higher priced.
Probably Las Lenas is the biggest/nicest. I think Bariloche is a bit larger than Chapelco, but last year Chapelco opened up several weeks before Bariloche (and Villa Angostura) as they had no snow yet. This year the official opening date is 18th June, but of course it depends on the snow.
We do a lot of cross-country skiing (with skins), which is great here, but that is also very good in Chile, especially on the volcanoes.