Actually....it depends on what you are going to use the miles for...Avis gives 700 miles per rental(no matter the length) for Qantas account holders. Anyone familiar with the award chart for Qantas will know that you can use these miles for flights on AA.
The chart is a little quirky though..the reward points required is determined by the distance you want to fly....0-2000miles RT is 20K in economy and 2001-5400miles RT is 30K in economy....so....for a trip UNDER 2000 miles RT Qantas is the BEST deal...requiring only 29 rentals. For a trip 2001-5400miles RT...it jumps to 43 rentals and goes up from there...but you also have to factor in that you will be able to fly to many more destinations with AA than you will with SouthWest...and you get MRTC as well.
Hope this helps.

P.S.- You don't have to fly Qantas to get these miles.I have been doing this for a while now and have close to 100K in my Qantas account (Hilton double dip goes there too...1000 per stay) and have never even set foot on Qantas metal.