Personally, I always use an Amex card (one actually from Amex, i.e., not an Amex issued by Citibank) when renting a car. I had an accident many years ago in a rental and Amex came through with flying colors.

I even use Amex when renting overseas where I would normally use a different MC or Visa with a lower forex charge. The difference is worth it to have Amex on my side if there is a problem.

By the way, the various Amex cards have different sorts of coverage. I personally use the Starwood, Costco or (when I had one) Delta cards.

As to the purported utilization charges, some states authorize them by state law, but, IMHO, they remain questionable--especially now when fleet utilization must be very low. There has been a lot of comment on this on various FT forums and on the web in general.