Not knowing if you own other firearms or are familiar with firearm makes, it's difficult to make a recommendation . However, if you have decided that you want either a M1 Garand or a pistol, my suggestion would be a handgun. The M1 Garand is a great Battle Rifle to be sure. It is tuff, heavy, and shoot a big round. You can use it for big game hunting or long range target shooting. If that's what you are looking for, then go for it.
However, for versatility I'd recommend a handgun. In that category, my suggestion is 1 of 3 types of handguns, either a 45 ACP 1911, a wonder 9, or a 357/38 revolver, depending on your level of skill and how much training you willing to dedicate to it. Any one of these rounds will serve you well. I like Single Action type handguns, but also see the advantage to DA/SA as well. I personally do not like DAO handguns.
My suggestion would be a good 1911 with a 5 inch barrel (Government Model). It's versatile, hard hitting, proven technology, and ammo is available everywhere. If you want a 9mm then get a Glock17/34.
Good luck in your choice.
Hooya