When you purchase a domain - either as part of the "Buy a domain" wizard, or when you purchase directly from a registrar - you are free to use any registrar that you wish, for the purchase. The "Buy a domain" wizard (which should be your preferred method of purchase) lets you use either eNom or GoDaddy - and which registrar you use is your choice - though the choice is not made obvious, by the wizard layout.
The selection of which registrar to use, in "Buy a domain", is always your decision - though the selection process is somewhat obscure. Just go slowly, and look carefully for the right link.
Start from the Good News display. Find the tiny link at the bottom - "Learn more", next to the name of the chosen registrar.
And, there it is. If you don't like the choice made for you, pick the other.
The choice is right there - you just have to know where to look.