The Australian because it looks solid. The other species look more like eels, whereas the Australian has a diamond pattern that is rather lizard-like and more pleasing in a visual-tactile sense. Also, the tall, stocky build speaks more of strength than stealth, which appeals to me since I am sometimes loud and outspoken (as some here have come to learn. Sorry).
I've never kept a lungfish, since I have to wait a few more years on a truly giant tank. But they are on the list!