Thanks for the input 😬
I'd suggest Vail. I've been to both and Mammoth isn't bad either. Pro/cons of each:
A lot of people on this site rip Vail due to "resort" village, costs and lack of exert level steeps. All are valid complaints but they do not seem to apply to this group.
You might also want to consider other ski areas including lots of options in CO. It all depends what you value from the above list. If you specify, we can suggest other areas too.
Just for fun I'll offer something of the other side, at least to fill in more about Mammoth. I've skied plenty of times in Summit County but never at Vail ($$$).
It sounds like you're intrigued by Mammoth. You should be! It's an interesting and somewhat unique place, because it's on the edge of the desert. From the top of the mountain you see desert to the east, Mono Lake to the north, and you can also look west and see the crest of the Sierra (basically the backside of Yosemite). It's quite a combination of contrasting landscapes.
Not sure how you're going to get there (Mammoth does have an airport) but the drive up from LA is spectacular too. It's low elevation, dry and sunny, through the desert, and for the last couple hours you get to look at a massive wall of granite that forms the eastern flank of the Sierra. If you're looking for a side trip, you can go to Death Valley. Much better in winter!
Mammoth has mostly black runs off the top, but there are a couple groomed black runs that intermediates can try. It's steep, but it looks worse than it is. If you're game to try something like Cornice Bowl, you can do laps on the gondola. Quite apart from the top there is plenty of skiing because though Vail is big (5200 acres), Mammoth is not small (3500 acres). Plenty of intermediate runs all around.
Mammoth can be windy, especially when a snowstorm blows in, but most of the time it's quite sunny and nice. My experience in Summit County was that it got pretty cold, even when it wasn't windy.