I have been feeding my cats Science Diet, but I've been reading some bad stuff about it lately so I want to switch....I've decided to go with Nutro. I just have one question...What's the difference between Nutro Natural and Nutro Max? I read the pamphlet and it says the nutro max is specially designed to reduce the ph level in urine (which is great cuz my cat is prone for UTI's) but which one is really better?