South American Puffer is the way to go. I have 3 of them in my community tank. They are awesome! Peaceful an very active. From what I've heard they are one of the only puffers that can be kept with other fish an their own kind.
Really depends on tank size and what you plan on mixing them with...
As mentioned south american puffers do well in groups but need around 20G each... Not to mention they are one species that WILL require manual teeth trimming...