The Dolomites and Sella Ronda I know very well, been there quite a number of times. I wouldn't say 'like the back of my hand', but I know where to find any kind of skiing and which village offers best opprtunities.
Personally, I don't care very much for the ultra steep or fast runs. I am more of a cruising kind of guy that now and again likes to do a very fast run. Zermatt hasn't intrigued me, if I am honest, nor does Chemaonix. The Cervinia side does appeal to mehowever, because it's one of the nicest cruising grounds in Italy, with the possibility to hop over to the Swiss side.
So, the Dolomites have my vote as well. And the Sella Ronda offers most chances of doing... everything without having to take busses or car drives. Arraba is the perfect spot, I agree. Or maybe Corvara: closer to Val Gardena with its beuatiful and more challenging runs (from Arabba, It takes 90 miutes or so to reach Selva, from Corvara that's 30 minutes) and it has great mellow terrain in the back yard. Great place. Selva in Val Gardena has most possibillities for accommodation. Last time I was there (March 2014) we satyed 50 meters from the bottom of the Saslong run, up on the hill in a nice house with 12 beds and a large kitchen: 2,500 Euro in total for the week. Split that with a large group, and gathering HQ has never been so cheap AND charming, I assure you.
So in short, I am all for the Dolomites. But I would also happily host a gathering in Espace Killy or Three Valleys in France, both of which I know quite well also. In every place we end up, there is the possibility to hire a guide a find great runs off-piste and in couloirs, don't worry. If the weather and snow conditions allow.