Wirelessly posted (BlackBerry8703e/4.1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/104)

I tend to use a World MasterCard, pricipally because it will still provide coverage even if I use a free-day or dollars-off coupon, as long as at least one full day's rental fee is charged to the card. Not all credit cards provide coverage if you use a coupon.

I'm not particularly worried about loss-of-use fees: if the rental company can't satisfy the MC insurer as to the legitimacy of such charges, I doubt that it could satisfy MC itself if I were to dispute the charge.

Administrative charges are more problematic, but at least for my rentals in New York State, it appears that state law does not permit the rental car company to charge this fee or loss-of-use fees.

The credit card LDW coverage is a big deal for me, as I do not own a car. For the OP, it's probably less important, as the cc coverage (except for that provided by Diners Club) is secondary to the coverage provided by his personal auto insurance policy.