Considering that neither of them are necessarily "great", you'd much rather feed them Purina One. Meow Mix is horrible - the first ingredient is chicken by-products. Purina One actually contains a little bit of meat, Meow Mix is nothing but carbs.

By the way, put some research into wet foods. How much does Purina One cost you right now? There might be better kibble that you could feed your cats for a similar price. Iams is a better brand generally but they're also generally more expensive.