For concealed carry, a .357 wheelgun - you can use either .357 or .38 rounds.
To start learning to shoot a rifle, a .22 Marlin or Ruger, and then eventually graduate to .308 or 30.06.
So a lot depends on what you want the gun for.
Slight ding. It's .38 Special rounds.
And I do enjoy occasionally trotting out the .357 for a few +P rounds on a desert range. No melon is safe from my wrath then!