The best days to visit any of the theme parks is during the week. We have annual passes for all the theme parks in Orlando and whenever we have a break we go on Tuesday or Wednesday. Sunday is slow too. These days are usually travel days. So pick any day during the week to experience the theme parks. Also a hint for you, If you have never been to IOA, visit Spiderman FIRST!!! It gets crowed and stays crowded. The coasters seem to never really have a huge line so you can do these whenever, but Spiderman and the water rides get crowded early. Have a great time!