I like the pranayama breathing a lot but with the I Am mantra for meditation I'm just unsure. Mostly because there's so many meditations to choose from. So right now I've narrowed it down to fallowing my breath (whice is basically every meditation in every tradition)and this I AM mantra.
I too am fond of the following of the breath and I use it to come out of meditation, and sometimes to prepare myself for the mantra. You can follow your breath all day if you like. It is a great tool for recentering yourself, for going to sleep, for all sorts of things.