Puffers are better as singleton in a tank. DPs have a good chance of surviving with each other since they are small and a hobbyist's tank is pretty big.
In a big setting, if there are very few decor, then the DP may try to claim every inch of the tank. If the tank was setup with lots of decor (making the tank look like it has a few isolated area), then 2 DPs could claim one of those isolated area. Territory is important for a DP.
Even for a 10g, you can never be certain that a DP will tolerate anything in its tank. You might have a really aggressive male in the tank with no tolerance to tankmates.