I have a bias toward small companies but I think my bias is well founded. The smaller the company the easier to develop a long-term relationship with your cleaner. That’s because turnover among cleaning employees is notoriously high, and is worse, I believe, with larger companies. The second reason is that with a small service, the more personal relationships that exist within their business are likely to inspire more attentive cleaning among employees.
Of course, the best service is one (like mine) where the owner is the cleaner.
With any cleaning service you are considering hiring, check reviews online.