I used to be a customer of VPI (now Nationwide) which, at least years back, used to be terrible. I was then a customer of Petplan which, at the time, was one of the best in the market, but there were still a few too many restrictions which hindered some medical choices (only improved upon in recent months).
So, back this spring, for my new dog, I pored over all of the available plans and, based on all that experience, Figo came out best, above and beyond. They've thought of everything (see the "Compare" chart on their website) and their premium (so far) is reasonable. I've had them since June for my current dog and already (unfortunately) have had to make several claims, and they've paid as expected, and quickly, and their customer service is terrific. Definitely put them in your mix when you research plans!