I have rented from Avis. Each time I've had a different type rental in each different city. Here are some details:

Avis.com/phone/counter rental: The hold will be for the estimated charges online or what the agent quotes you. This doesn't include coupon deductions. The coupons are deducted AFTER the rental. For example, if I had a week reservation for $272.93 with a $30 off/week coupon, there would be a $272.93 hold on my card. When I return the vehicle, the charges to my credit card will be $242.93. For a debit card, I have been told $500.

Priceline and Hotwire: Since it is prepaid, $100 hold on credit card. $300 hold on debit card. If you ask for an upgrade, usually they will give it to you for $3-$10 more a day per car class, but the $100/$300 hold still stays the same.

Online agents (Orbitz, etc.): Same for Avis.com above.

I have heard that some locations like JFK, LGA, ORD, LAX will not accept debit cards, but I am not sure.