Kirkland diapers at Costco are 100% fine (my child has sensitive skin and we always used Pampers before). Honestly though, try the cheapest diapers (Luvs? Target store brand?) and if they don't give your kid a rash, just stick with them.
My DH's family were diaper know-it-alls and we started out with Pampers due to peer pressure from them (we were the last to have kids in the family).

Then switched to Kirkland later on.