Other Car Rental Programs/Partners (ie. Alamo, Enterprise, Sixt) - Pls give me suggestion to rent on this trip

Hi all,
I would like to rent a car as following destination, how to make it into cheapest method? any coupon can suggest to me?
1. Seattle to San Francisco
2. San Francisco to Las Vegas
3. inside Las Vegas
4. Las Vegas to LA
5 inside LA

thanks in advance