I would recommend a registrar that would explain to the customer why they would not want a .me domain for anything critical unless the person lives in Montenegro and trust the Government of Montenegro to maintain a good and trust worthy registry.

Otherwise just use which ever registrar is cheapest and who you think will handle any quirks or shenanigans that registries may do to domains you own, and which own system and processes hold high enough standard for you.

porkbun are great

squarespace is legit. GCP cloud domains are moved to them.

I've never had a problem with Namecheap but I'm not sure they are really any better as I've never had a problem with GoDaddy either.

Dynadot. One of the largest registrars, and very competitive pricing like Namecheap. They also have very good features.

I'm quite comfortable with Netim

I’ve been happy with Gandi.net for years now. They’re based in France.

porkbun

AWS Route53 or Namecheap

Cloudflare

Cloudflare