my clown knife outcompetes both my tsn and my gar for food - the key is to get them to except all sorts of food, live, frozen even pellets
i would stay away from the dorado - i had one in w/ my clown knife and gar and he was a non-stop terror and he was smaller then both of them - the dorado constantly attacked the knife and chewed up his tail and eventually put a large open wound on my gar - awesome fish but not something you want to keep with tankmates
I currently have mine with 2 puffers, I think they've all learned to get along cuz I saw the clown chase a puffer around last week... I think they've been neutral since!