I'm with Fella on this. Only two species of puffer come anywhere near being reliable community fish: SAPs and irrbuesco (red-tail) puffers. Neither are 100% safe, but most work out pretty well with the right tankmates. Plecs seem to work with both, as do Ancistrus, Otocinclus, Panaque, etc. I would not risk whiptail catfish though -- I suspect their long tails would just be too much tempation.
SAPs get to about 8 cm in captivity, and will work fine in any tank big enough for a plec. A common plec should be kept in a tank at least 1 metre long, which will give an SAP ample swimming space. Bristlenose plecs (Ancistrus spp.) can get by with less, but even a 60-80 cm tank should be acceptable for an SAP provided you install plenty of water current. SAPs are river species and have an instinctive need to swim all day long. The only time they rest is at night, when they settle onto the sand (or in it, sometimes).
Red-tail puffers are rather shy, difficult to find in the shops, and often expensive. They are lovely puffers though, once settled in. Some seem a bit delicate on import, and need lots of TLC for the first few weeks. A few specimens have been reported to be fin-nippers, but most seem to be placid and easy-going when kept with appropriate tankmates. Don't mix with guppies or angelfish, for example, but anything fast-moving, like tetras and danios, will be fine.
As Fella said, the downside to SAPs is that they have very fast-growing teeth. To some extent snails will prevent the overgrowth of these, but people's experiences do vary. I find snails do the trick all by themselves, at least to the degree where there is little growth even in an entire year. Others find this not to be the case. Perhaps the type of snail used, and how often they're provided, matters?
On the other hand, IMHO, the SAP is by far the toughest of all the commonly traded pufferfish. It's the least affected by pH, hardness, salinity, or nitrate levels. What it does like is a mature filter, strong water current, lots of oxygen, non-aggressive tankmates, and one or more companions of its own species. My only bad experience with this species was losing one after it "bruised" itself after throwing itself around the tank.
Cheers,
Neale