Start with the mountain, not the logo
If your home hill is Park City, Vail, Breck, Keystone, Heavenly, or Okemo — Epic. If it is Brighton, Solitude, Alta, Snowbird, Deer Valley, Steamboat, or Winter Park — Ikon. Buying the other pass because a podcast said so is how you own a very expensive coupon for the wrong canyon.
Family features are not evenly distributed
Epic's family strength is Park City + Keystone Kidtopia + Okemo Jackson Gore + Breck town. Ikon's is Steamboat Vacation Center + Deer Valley Children's Center + Winter Park Discovery + the Cottonwoods. Smugglers' Notch isn't on either, and it might still be your best week.
Kids' pass pricing
Both sell child products that look cheap until you read blackout dates and 'days at destination' caps. Read the current year's PDF. I am not reprinting last year's numbers as if they were a covenant.
Two-pass families
Some of us end up with both over a few seasons. It's not elegant. It is sometimes cheaper than window tickets at the in-law mountain. Do the actual days. If you are a once-a-year family, one pass or a package at Smugglers' will beat a drawer full of barcodes.