IOA...it's a little small, but the rides are incredible. Some of the best I have been on. If it is hot, go on Dudley Do-Rights Ripsaw Falls...the best flume ride I have ever been on. Dueling Dragons and The Hulk are world-class coasters.
You have to like zoos in order to fully enjoy BG. But their coasters are excellent as well. Both parks are great! But go to IOA, you don't know what you are missing if you don't go on Spiderman.