I currently host domains with the following registrars:

• Cloudflare Registrar - At-cost domains, but limited number of TLDs
• Porkbun - Cheapest one for most nTLDs
• INWX - Cheapest one for my .de domains
• Versio - Cheapest one for my .eu domains
• OVH - Cheapest one for one .se domain I own

My requirements for registrars.