I carry the M&P9 2.0 with the 4.25" barrel and tritium sights, the new ones fixed the trigger issue that a previous member posted about. My recommendation would be to go to a local range as most of them around here do a rental program where you can pay like $10/hr and shoot their guns but you have to run their ammo through it (which can be a little more expensive). This way you can see which is more comfortable for you to shoot. Keep in mind the M&P9 2.0 comes with changeable hand grips so you can change the comfort level if that's an issue.

I also agree that training is the most important thing no matter what you go with. look into any local courses that offer more advanced training or get involved with you local gun club that may hold competitions. I have found steel shooting competitions to be a huge training aid because it helps put you in a little higher stress situation as its timed and depends on reasonable accuracy plus everyone is usually super friendly and willing to help with any form issues you might have.

Next step: Holster. Go with Aliengear. You wont be disappointed.