Polomarc, I note you are UK-based. If I were you I would seriously consider using a UK company rather than a US one. You'll be entering into a contract under UK law. If things go wrong you can resort to regulatory bodies (or the county court) here in the UK. You are covered by UK/EU data protection rules.

The two on your shortlist are not UK-based. Domainmonster, whom you mentioned in your first post, is a UK company.

Price isn't everything. I'd rather pay a bit more and deal with a company that's under the jurisdiction of the country that I live in.