I use Gandi for domains & DNS too. I've never had any problems so far but I don't want any surprises... Where do you want to migrate? What is a better alternative?
I like Cloudflare and find them to be a very good value proposition. They have a domain registrar now as well, though I haven't tried that yet. https://www.cloudflare.com/products/registrar/
I moved a couple Namecheap domains to Cloudflare's registrar when they launched, no complaints here. One domain took a bit longer to transfer, but the first took only a few minutes so I didn't mind it at all. I already used them for DNS so it felt like a no-brainer.
I'm using Porkbun and like it. I've used Namecheap, Cloudflare, Alibaba Cloud, and Gandi. I prefer Porkbun to all of them, but I'm a fan of simple, no-frills stuff.
I've used support twice when transferring domains into Porkbun and they were good. I transferred a domain out and has no issues. Their 2FA options are really good. They frequently have the best prices around (tld-list.com).