I've been reading a bit about this, and nearly everyone seems to recommend a 3:2 ratio (inhale for 3 steps, exhale for 2 steps) changing to 2:1 on more intense sections.
I've been doing 2:2 - at least partly because I run to music, which usually has a 2/4 or 4/4 beat. It's very hard to run 3:2 to rock music.
Even on the rare occasion when I run without music, I find the 3:2 hard to maintain. It just doesn't feel natural to me.
Is there any benefit in changing?