Frequent flyer miles/points for rental cars are generally not a good value in my opinion. With the added surcharge that most rental companies add when you get the points/miles you are paying way to much.

However they are a way for the infrequent flyer to keep activity in a frequent flyer program. Of all the airlines I think the best deal is getting a half a credit per car rental, except when there are airline promotions.

I think signing up with a loyalty program with your car rental partner is a better option, as you will get free rental car days after so many rentals. After you get enough free rental car days to use with your free airline tickets I would stick to that. After you have enough then start taking Southwest credits.

I primarily use National which isn't a Southwest partner. I have been using Avis quite a bit recently and have been taking the 0.5 per rental credit, as I have more than enough free days saved up at National.

One thing about Avis is they give you the credit quickly. Last couple of rentals were credited within 48 hours. When I got the emil from Southwest about another award had been deposited to my account I couldn't figure it out, as I hadn't been on a Southwest flight in a while, and I couldn't believe Avis had sent the credit on so quickly.