Sometimes the choice of procedure is driven by other concurrent surgical requirements. When I had my valve replaced, I also needed a bypass, so they did a full median sternotomy. When I expressed my chagrin to my surgeon, he promised me that the recovery and pain levels were the same with either, and with the full sternotomy he would have better access to do his job. I was satisfied with that reasoning and told him so.
The other dimension to the incision is the cut itself. Different surgeons use incisions of different lengths to do the same op. My incision scar is only about 4 inches long, and the surgeon ran the cut on a slight angle so that the top of the incision is off-center. That way, if I wear a shirt with the top button open, the scar doesn't show. I didn't ask for these "features" but I did thank him for his consideration afterward.