For Range
Home defense
and Carry
The answer to this one depends A LOT on what you want to do at the range and how well you can conceal a handgun. Often those three purposes are mutually exclusive.
What do you intend to do at the range? If you are just blasting at 7-10 yards a carry gun might do. I don't like doing that with my Mod 36, but then I don't try to carry my full-size handguns either. Sounds to me like you need more than one. I'll suggest a .22lr pistol for the range. Get a lot of ammo to put through it honing your skills and then get a centerfire pistol in .38, .357, 9mm or .45acp for ammo availability and then start practicing again. I'm in the camp that believes handguns are marginal for home defense and suggest a 20" shotgun in 12 or 20 gauge for that.
So my short answer for the "only one pistol" question is a quality .22lr pistol. Ruger, Browning, and S&W all make good examples.