Both are more lurker species of puffers, although my Congo, (T.Miurus) tends to be quite active and very rarely buries himself unless the lights go off or he's attempting to hunt...
As for the Suvatti, same thing, they are known to bury themselves, although each puffer has its own personality and may or may not bury themselves...
But with that being said, the do prefer a substrate bottom (with no sharp edges) so that if they decide to do so they can bury themselves without getting hurt...
Any way for pictures and more info check out these two links:
Suvatti: PICS
T.Miurus: PICS