Begin by asking yourself what you need it for. For example, if you plan to drive through a large slice of America, you'll want to be able to get speedy emergency service and perhaps a replacement car almost anywhere. If you'll travel only within state, however, a smaller company may be preferable because it charges less. But be sure that you won't need help from the company after hours. With an off-brand company, incidentally, be sure to inspect the car meticulously for damage before you drive away, and have each nick or scratch noted on the rental contract.
Smaller companies tend to be fussier about such blemishes than the biggies.
If your trip will be mostly by air, with drives between flights, you'll want rental facilities within or close to the airport terminal, and frequent shuttle transportation. But if you'll pick up and drop off downtown, you may prefer a company like Enterprise with neighborhood offices, which will take the car to you at your workplace, hotel or home and pick up when you're ready to return it. For frequent renters, it may be worthwhile to join a company's premium program that offers frequent customers a host of minor conveniences. Be aware that you are often limited to one discount per rental. Auto rentals are typically charged to personal or corporate charge cards, such as Visa, MasterCard, Diners Club or American Express.