Other Car Rental Programs/Partners (ie. Alamo, Enterprise, Sixt) - Which is the best rental car company for 14 day rental

I need to rent a car from tomorrow (2/28) at LAX for 2 weeks and wanted to know which company to use, what size car to get, and, crucially, which one has the cheapest liability insurance (I've been using flexcar so I don't have insurance)?
Also, how much should I pay for satellite navigation?
jason

I'd check out some of the multiple-search engines, like Orbitz to see who has the best general rates. Regarding insurance, many credit cards offer insurance if you pay with them. Check to see if any of your cards offer this. In order to activate this you usually need to refuse all of the insurance the rental company offers. Regarding GPS, I've seen them offered for $10/day or so. For only a little bit more (http://www.thegpsstore.com/Detail-Garmin-StreetPilot-i2-car-gps-system.asp) you can purchase one of your own.