We use Alamo as well. They usually have the lowest rental fee and we find it a lot more convenient since they're located at the airport terminal and their pickup/return process is really easy as well. Alamo also offers airmiles.
If you do go with Alamo --- we've found we get the lowest rates booking early but keep an eye on their website since they frequently offer $$'s off codes that you can apply to your rental. If you see a better deal you can always cancel your original booking. We prefer to book directly through Alamo because you then have the flexibility to change companies, car size, etc... without penalty (unlike some of the travel sites).
We never get the added insurances. For most people their regular car insurance will cover them pretty well (but you should definitely check with your insurance company first. We also have a credit card that covers the CDW component --- but I don't think it covers Third-party aspect.) There are also lots of gas stations near the airport so we always forgo their deal to return the car without filling up.
Whichever company you go with, if you reserve online make sure you print off the summary screens (with amounts, etc...) to ensure that you get the deal you signed up for.
Have a great time...
