I play them both and sometimes I'll just use the Octave way to play the power chord....

Ex

e--X
B--X
G--X
D--3
A--X
E--1

Or just the root 5

Ex

e--X
B--X
G--X
D--X
A--3 (4)
E--1 (1)


What I found is that they can all work but the deciding factor on which "one" to play will depend more on what the rhythm is doing.

If you are only playing "short" intervals of the chord and it is up-tempo thenthe 1 ,3,4 (fingering) works, or the 2nd example for root5.

The barred way I tend to use more for "sliding" up to the chord and for songs that need the chord to hold longer. It is more of a matter of personal choice. I beleive in learning to play chord all ways and shapes and let the "song" dictate the way you play the chord.

In a nut shell-- Learn each different way accordingly.

2 cents