My main criteria were: fair prices without any coupon codes, no-upselling, free whois privacy as standard, most ccTLDs supported, REST API for everything, and at least 15-20 years of history.
I would normally prefer a European company, but Dynadot has been the registrar of wikileaks.org since 2006.
They are a major registrar with many millions of domains registered through them.
I had some domains registered through Gandi in the past, but they're prices are kinda high, and their web interface isn't that great.
When we acquire a new domain, I just file it in the appropriate folder and all my templates are automatically applied.
Free privacy and DNS is a nice extra. Reduces spam and overhead.
I’ve also heard good things about Gandi.net but I haven’t tried them myself.
But its ownership has changed multiple times over two decades, and the company is now owned by a private equity firm. The most recent reviews have been far from great[1].
I would recommend INWX (Germany) as the best European alternative to Dynadot.