In terms of aggression I don't think there are more or less aggressive morphs to avoid. If you're talking about overall behavior I would caution you about the few wobble genes (spiders mostly, but also woma and champagne and possibly some others I'm forgetting). My lesser bee has a pretty bad wobble and you can definitely tell by looking at him that he's a little "special". He does not sit still while being handled and moves oddly, twisting back on himself and sometimes corkscrewing (it's not uncommon to find him with his head and neck twisted back in a "c" shape even while he's just alone in his tub). It doesn't effect his quality of life and he's still able to eat and breed perfectly fine, but if I wasn't aware of the spider wobble when I got him I would have been very unpleasantly surprised by what I received.