I am a flip flop person and soon as the weather is nice each year, I wear them every day. Because of that I wear the croc flip flops (sooooo glad when these came out). Our WDW trip in 2008 was for 10 days and I wore my croc flip flops all day every day and we were up early morning until closing during magical hours at each park. My feat were just fine! And let's not just worry about water parks or rides--don't forget those rainy times/days! Flippy flops were awesome!!
But it really is knowing what is sensible for you. I like the croc family (no matter how stupid many people think they are) because they work! If you are on your feet for long periods of time, they really are comfortable and rarely do my feet hurt. But if you need really good arch supports or whatever, then it would probably be best to go with a really good walking shoe.