I'd say it depends on what type of shooting you are doing. For many people standing and kneeling shots can be most challenging, so I'd say anything that strengthens your core. Personally, as an older shooter with arthritis in my hips and shoulders, and a bad back I think Pilates is absolutely superb. My core is stronger than it has ever been and my flexibility (given the shit state of my joints and spine) is good; I knock over free-standers on an HFT course fairly regularly with my TX200 which weighs in at 13lb.