I can speak from my own personal experience.
Background: Live in FL (This is important because some states restrict which policies can be sold), have pre-existing condition, and probably end up cancelling at least 1/3 of all trips that I have booked for health reasons. All of my claims have been paid although it requires a cumbersome and time consuming process to submit all the documents and support.
For the past 10+ years, I have used Steve Dasseos who owns tripinsurancestore.com (I have no affiliation). He is located out West and deals with clients all over the country. I like Steve because he sells whichever insurance carrier is cheapest for your particular needs (not locked into one carrier) and also only uses companies that have a proven track record of paying out their claims.
As a general rule, the basic policies cost 6% of total trip cost and Cancel For Any Reason - CFAR (75% reimbursement) cost 8% of total trip cost.
I hope this helps and doesn't break any forum rules by posting his name & company.