Just as an fyi on the lyonsi. A very mild Amphilophus species. They do have some pretty high conspecific aggression, and males can be pretty hard on females. But as far as I can tell with my pair, these guys don't much bother anything else. Not in my tank, anyway. Of course, they are in there with an oscar, vontehillo, and female festae... all fish that can protect themselves pretty well.
All of that said, I certainly agree with the above that specifically, the bocourti or pearsi are ideal choices, as gentle giants, that can hold their own if anything tries to bully them, but otherwise, are puppy dogs.
-Rich