There are some triggers considered more peaceful, such as the niger or blue jaw, and a few others. I have a niger that does relatively well with some of my less aggressive fish. He can get a little over excited at feeding time, but that is about it. The only other two things I would take into consideration when having a trigger is you are taking a "chance" with your inverts, and the fact that they can get quite large (for example the niger with a potential of 20") so not only is a large tank required but also good filtration.