fiends are actually programed to be stronger than powder gangers in the game, i think. so i vote fiends, since they are stronger, innumerable, and psychotic.
Fiends would whoop the crap out of the cons. There better equipped and jacked up on psycho, med-x, jet etc... If the fiends got there hands on a Cache of Power Armor... The fiends would wipe out most any "lesser faction" giving exception to the BoS
Fiends have the advantage. Better weapons, better numbers and their HQ is even more secure than the Powder Gangers. Not to mention, they are doped up all the time and crazy.
Powder Gangers are better organized and can keep even NCR at bay. Who needs energy weapons or chems? ... I'M T.N.T.! I'M DYNAMITE! I'M PUBLIC ENEMY N. 1! ...