h is the best characteristic that distinguishes the kingdom Archaebacteria rom the kingdom Eubacteria?

The answer is cell wall.

The best characteristic that distinguishes the kingdom Archaebacteria from the kingdom Eubacteria is the cell wall. Archaebacteria have cell walls made of uncommon lipids while Eubacteria have cell walls made of peptidoglycan. Speaking of structure and body type, both kingdoms include prokaryotic and unicellular organisms without differences in nutrition source, they could be autotroph or heterotrophs.