All 3 great schools - I have visited all of them several times. ALL have great endowments - they are in the rarefied air to have endowments of > $1 million/student.
My reco is Williams, but I am biased as I will have one son there now and another joining him next year.
Pomona seems to be the most proud of attracting the most diverse student body (58 countries in ~740 admitted students!). And the least snobbish, although this is obviously subjective.
We loved it so much that we agreed to D’s applying ED1 there, and then to paying almost full price for it, despite D’s decent chances at schools that would be much more generous to our demographics.
Ontario airport has Southwest flights so hopefully it won’t be awfully expensive, easy to find out.