Here's my two cents worth. I have kept most of the fish listed on this thread at one time or another (or have friends that have). I would say that the GATF is an incredible fish with amazing speed, teeth and predatory skill but is so shy and nervous (at least in aquariums) that they would never qualify. I have never seen a really bad aba aba (although I have heard stories of them being fairly nasty). The goonch catfish (Bagarius yarrelli) that I currently have never does much of anything, and although a fascinating species to maintain, has never attacked anything that was larger than a goldfish. I guess if one were to keep an adult specimen it could pretty much eat anything, but would still not be a super mean, bad, vicious fish. A big territorial male Dovii would be close to the top of my list, and I have seen them destroy almost any fish put in with them. But a large snakehead or aimara (black wolfish) would carve out about a 5 inch wide chunk of meat out of the dovii and that would be the end of that. So my pick would be either an adult red (giant) snakehead or a Hoplias aimara. I personally have never seen the equal of a pissed off adult aimara and they have the size and dentition to back up the attitude.