I've always liked the results I got by running ORTF with the elevation of the mics set at the average between the source of the vocals and the source of the guitar. That way, you capture some of the space in which the performance was recorded. If you're not within about 10 feet of the sound sources, then I'd recommend running the mics higher up to avoid chatter.
I've never been happy with separated tracking when there are only two sources. You can mix it to stereo, but you completely lose the space in the room. I like for my recordings to put the listener in the room where it was recorded, not simply bring the sound sources into a new room.