We get ours through our corporate insurance package as an add on to our health insurance, we only had the one option, i'll have to ask my fiancee who the company is exactly. If you can't get it through work there's a good number of customer satisfaction articles written about a lot of the popular ones.
I used healthy paws myself for a few years before I met my wife and was happy with them, I had to put my dog down due to cancer and they were amazing to deal with, and sent a condolence package as well. This was about 8 years ago now so things may have changed, I believe pet insurance popularity really took off in the last 5 so I expect that there's a pretty big difference in things.