Gandi is a no-nonsense service:
* Seems very security-minded, and overall serious and professional. Nothing like GoDaddy.
* Their UI is conservative and well-organized; not as modern as iwantmyname.com, but not as antiquated as EasyDNS and Namecheap (and not a jumble of different, conflicting, confusing UI styles like the latter is).
* Supports (in fact, requires) zone versioning so you can always undo.
* Supports raw "BIND"-format zone files so you can quickly edit in your favourite text editor, rather than a cumbersome web form.
* Lets you share the same zone file across multiple domains. If you need more automation (eg., lots of very similar domains with a slight tweak here and there), just use the APIs.
* Great APIs.
* 2FA account security.
* Also provides SSL (cheap, toplevel CA) and very good, reasonably priced virtual hosting (US and Europe).
iwantmyname.com has a more minimalistic, modern UI, but lacks things like zone versioning, raw editing, and they're still working on an API. Also, their 2FA is apparently SMS-based, won't work with a standard authenticator app.
We previously used Namecheap and EasyDNS. No significant complaints, but their UIs are horrible.