i would go for the Purina One based on price and ingredients, as others have mentioned. on the Yahoo Groups FLUTD group i belong to, the Purina One Urinary Health Formula is used by alot of members. one member even started on the ProPlan UT Health formula but switched. he said the difference in ingredients wasn't much and the kibble shape was smaller with One. i've also noticed ONE tends to be more available than ProPlan in my area.