What are good species of snakes for first time owners?

My mom said I can get a snake. I’m wondering what type I should go for. I have a 21 gallon tank. I’m looking for a snake that as an adult is about 3 feet. Is my tank big enough or do I need a new one? Also I can’t have a venomous one. I’m most comfortable with a snake that eats mice, but I’m flexible with that.
I’ve been researching and so far on my list of snakes to research further are:
black snake, king snake, coral snake, and milk snake. Do you guys have any ideas of good first time snake owner snakes?