I started power chord work recently and want to be sure that I'm not developing a bad habit that I'll have to un-learn later.

The video lesson I used said to finger power chords on the bottom three strings by taking an E-shape barre chord and leaving off the middle finger (and playing only the bottom three strings, of course). The index finger forms the barre and the ring finger and pinky each hold down one string. This can be moved over to the next three strings to do power chords on A D and G.

While messing around tonight, I figured out that I could also make power chords by an index finger barre and holding down two adjacent strings with my ring finger (I'm sure I'm not the first person to ever notice this). This seems a lot easier, especially when moving to higher frets where it was hard to get two fingers into the space. My question is, should I keep playing power chords with a two finger technique or is there a good reason to practice with the E-shape barre chord method? I don't want to ingrain a technique that will eventually be a hindrance to my playing, even if it works at the level I'm currently at.
I use two-fingered power chords all the time. And I also add the octave (three-fingered) at other times. It depends on the sound you want. With just a basic two-fingered power chord, the sound is a little more cutting and raw -- nice for very quick chord progressions. But when I want the chords to ring out a little longer, the full power chord with the octave added sounds thicker and more harmonically complex.

It's not an issue of there being a "right" and "wrong" way to do it -- they are both equally valid tools to add to your belt.
The poster above is absolutely correct. Most people either use full chords, two finger power chords, power chords with added octave, or all of the above. Don't worry about this, you're doing absolutely nothing wrong here. Have a nice day.
I just want to be sure that I was clear, In bothl cases I'm talking about three-note power chords (root, fifth and octave) but instead of using one finger each for the fifth and octave notes, using the ring finger to hold down *both* the fifth and octave strings simultaneously.

Just to be sure, does this change the answers? If not, I'm good to go.
that's great, if anything it's better than three finger because you're building flexibility in your ring finger. Being able to press two strings with one finger is useful a lot of the time.
Both / all ways are useful and you'll see why the more music you play.
Powerchords with fingers 1&3, 1&4, 2&4, 1&2, barring octave or using 3 fingers - pretty much any combination you can comfortably make - they all have their place and usefulness depending on what you're playing and what you're gonna play next.
you're probably gonna want both. but you don't really have to do this consciously. eventually you may run into something that requires you to do it a certain way.

that said, most people do it with three fingers.
Quote by archerygenious
Jesus Christ since when is the Pit a ****ing courtroom...

Like melodic, black, death, symphonic, and/or avant-garde metal? Want to collaborate? Message me!