It depends on other instruments in the song and how you want the guitars to sound in that particular song. sometimes its hard left and right, sometimes its 80% left and right, sometimes its 50% left and 100% right and so on. If you are the producer and mixing this song, I would try some different panning positions and see what works best for that song.
Each song will have different needs, so take each song on a case by case basis.
CJ