I'm going to stick my neck out and disasgree here.
While puffers are often best in single species tanks, that isn't always the case. I've been keeping a South American puffer in a community tank for 12 months now, without any serious problems. Certain fish were nipped, platies and Corydoras for example, but they were removed. Fast-moving things like halfbeaks, tetras, and glassfish seem to be fine.
http/www.fishforums.net/index.php?showtopic=143552
http/www.fishforums.net/index.php?showtopic=144843
It is also apparent to me that South Americans are much better kept in groups and not singly. Since getting two tankmates for my original specimen, they have proved to be much more outgoing and brave. In short, more fun.
Pufferfish are predators, but very few are piscivores. Most (almost all) feed primarily on shelled invertebrates; snails, shrimps, etc. The confusion comes from the way they feed. If you watch them in the wild, you will see that they swim up and down every object they encounter, studying it closely, and searching for their prey, which is usually well hidden. They want do the same thing in captivity. Puffers kept in empty tanks with just one bit of bogwood get bored. They need lots of objects to explore, whether plants, wood, or caves. Nibbling on a fish is to them the same thing as nibbling on a bit of rock, to see if it's really a bit of rock or actually an oyster or something. I don't actually believe they want to eat their unfortunate tankmate.
This approach has worked for me using both the South American and the red-tail, red-eye puffer, a pair of which I have living in a 10 gallon tank with some gobies and Danio choprae.
Cheers,
Neale
Puffers, any type of puffer, are species only fish. True some might do well in communities for a while, but being predatory fish chances are Very high that your fish will get eaten at some point.