On Wednesday, December 16, 2015 at 8:51:46 AM UTC-7, Jonathan St. Cloud wrote:
Turns out there are only two underwriters no matter how many quotes you get. Costello was the lowest by over $300 with an AOPA membership.


There are more now: I found this from a 2014 article:

"An explosion of growth in aviation insurance underwriters brought new
entrants to the market over the last four years. International Aerospace
Insurance Services, Berkley Aviation, Allianz Aviation (US), Starr Aviation
and an expansion of Lloyds are some of the newer players."