Any fish can be the best type for a pet, but that is based on what you can afford, what you can maintain and what you think is good looking.
If anything, a Betta in a 5 gallon, filtered and heated tank would be a good idea. Always fishless cycle prior to adding fish, make sure the filtration doesn't cause too much current and the heating is between 77 and 80 Fahrenheit. Check out the link for Betta care.
Goldfish on the other hand, money wise, are harder to maintain. They need a large tank and double filtration in order to be happy and an already cycled tank for the best chances of being healthy.
When you think of it, there is such a wide variety of freshwater fish to choose from that can be your best pet, but it's totally up to you to research as much as possible about it in order to have a happy and healthy wet pet.