Whatever you choice to get. It must be available and carry well. I have found that a good vertical shoulder rig will allow you to carry anything you want. I have carried a S&W Model 28 with a 6 inch barrel with a fully loaded framed back-pack and it worked very well. T shirt and a light weight nylon windbreaker over the rig. If you slip while climbing the backpack will take the impact and not the Gun.
Good luck on your selection.