I rent a lot from Hertz and Avis--they have unlimited mileage if you stay within the state (and sometimes neighboring states). Here are some pointers:
1) Make sure you fill up the gas before you return. The car rental companies have been really strict recently on this.
2) If you have good car insurance, go ahead and decline the additional coverage that they try to sell you.
3) There are often a lot of fees and taxes imposed by the government. These are unavoidable, but find out ahead of time because they add up to a lot! (Stupid NFL and NBA stadiums are often subsidized by hotel and car rental taxes :| )
4) I find that the major car rental companies are more liberal with their policies, so it may be better to pay a little more for Hertz or Avis than suffer with Enterprise. The cars are also cleaner and in better condition. Try to get a discount--Do you have AAA? Airline frequent flier memberships? Govt discount? Also, weekend rates are lower.
5) When you get to the rental booth-ask for a free upgrade--you never know . . .
6) If you are underaged--meaning less than 25 or 26 years old, you will probably have to pay a dangerous driver surcharge
edit: Regarding minor damage to the car--Hertz and Avis barely blink when you return the car. I don't worry about damage unless it's major. Again--I think the cheapo car rental companies are stricter when it comes to "damage"