According to viamichelin.com there's just half an hour of difference between Livigno and Masco Corto.
Perhaps the main difference is that to South Tyrol the road is mostly by highway.
Anyway Val Venosta can be a good compromise. Slopes are not crowdy at all, i've been there there 3 years ago just after new years eve.
The are three resorts with an unique skipass:San Valentino / Belpiano / Nauders. The last one is in Austria. They are connected by bus.
I didn't visit Nauders. Between San Valentino and Belpiano, no doubt in choosing Belpiano, is a bit bigger and thera are more slopes for beginners