The Largemouth bass I have had are not aggressive as in bullying other fish. They are aggressive when they eat and will eat anything that fits in their mouth but they aren't super territorial. I caught a 14 inch largemouth on a 8 inch swimbait last spring..... Like Hoyo said I think Green sunfish are the most aggressive. I had some in a pond and they are hands down the most aggressive fish I have ever seen, they killed off all my goldfish and koi during spawning season.