I was with Intertek for several years, and had no complaints. No experience with SAI. They're both huge, and well established, so it's probably a toss-up.
That being said:
- Reviews are often based on interactions with individuals within the organization. Sales people, account managers, and auditors can vary tremendously within any given organization.
- Our needs were simple at the time, and everything always went smoothly, so I can't comment on how they deal with issues (complaint resolutions, challenges to audit findings, etc.) which, I imagine, distinguishes good from bad.
Some advice:
- Plan ahead. You might only need one service now, but in the future other services might be needed (e.g. as you expand to other markets). Inquire about their other services, and try to pick a registrar right off the bat that can provide as many of the services you may need into the future. Having to only deal with one organization is far easier.
- Don't judge organization by interactions with sales people. They are always eager and responsive - this may not necessarily be the case once they have your money...
Good luck!
MM