The statement that 9mm ammo is just as effective as 40 might apply to practice, but is not supported by the facts regarding self defense.

If you want a good semi-auto for practicing with, Glock has several models that fit the bill. If you want a good semi-auto for self defense, pick one that shoots the largest, most powerful cartridge you can reliably handle. For some folks, that may limit them to a 22 lr. For others, a 45 auto will be a better choice than lesser cartridges, such as the 9mm and 40 S&W. It's all a matter of ability and committment.