I have been with Hilton for years and I double dip with both going to the Hilton programs. Why have 500 points go to UA when you get thousands more points added to your Hilton Honors account.
I like the variety of hotels in the Hilton chain. I travel to Europe several times a years and find Hilton family hotels about 70% of the time. The perks for Diamonds are good. I am upgraded about 80% of the time; some of them fantastic like paying for a single and landing a suite.