GBR's are an awsome looking fish, yes. But they are also more susceptible to water conditions as well. A few members in AA have been having problems with them dying. So if you go with the Bolivians, they are a lot more hardy. I have Bolivians in my 29G with cardinals, bleeding hearts, serpae's, and blue flame tetras, and none really school much. The only aggression displayed by the Bolivians is the male chasing tetras out of their breeding area. Other than that, no threats.
Now if you are interested in fish that school much better, then I would have to say Rummynose Tetras. Mine are always together. Very seldom do they ever split up. Out of all the tetras I currently have, I would say they school the best. And for larger fish, my Roseline Sharks are excellent schoolers. But you need a bigger tank for them.