What is a good quality cat food to switch to?



Ive read innova EVO and wellness are good but they are hard to find where i live and ive also read they can be bad for cats with high protein intolerance. Im thinking of buying Avoderm or California natural. are those ok? they currently eat purina cat chow. Also, do i have to feed them a certain amount? Since i have a lot of cats I usually just pour food on the dish and they come eat when they want.