Though I've been a web developer for a fair amount of time, I am going for the first time to buy a few domain names. I have looked into the domains I'm going to buy and know that they're available, and I've been looking into which sellers to use. After doing a lot of research, the main ones I'm considering are 1&1, Namecheap, and Gandi.

The problem is, when continuing to research, I'm not really sure what makes one domain seller distinct from another. I don't need much in the way of services--definitely not hosting, since I plan to use Heroku for that. I mainly only need the domain itself and DNS management, as well as possibly SSL certificates and WHOIS protection.

Question:

What makes one domain seller different from another? How can I go about evaluating which one is the best for me?

Note: This question is not which domain seller is the best, but rather, what criteria can I use to evaluate them and rank one over another. I'm trying to find out what makes one domain seller different from another, since they all seem to be pretty similar to me right now.