Opinions needed: Best extended auto insurance policy company?

I’m looking into buying an extended warranty for my car. I purchased an extended warranty once before, a number of years back, and although it looked like it covered everything, I found out the hard way it didn’t.

I’m looking for your experiences and opinions (both good and bad), and what company you’ve used and had any service issue covered. Say your automatic transmission died, or your AC unit.

Thanks for your opinions!
SFP