FWIW, Southwest's standard (saver) award availability has been decent of late. The online booking engine shows availability accurately, and seats often open up a week or so before the travel date. Changes are free of any fees, so you can keep fine tuning your trip. Yes, it's frustrating having to wait so late to know whether you will get the flight, but it's better to get a seat this way than not at all.
From the Southwest website:
Each credit is valid for 24 months from the date earned. Your Rapid Rewards account will contain only valid credits collected within the immediately preceding 24 consecutive months. If a credit is not applied toward an Award within 24 months of the date earned, it will be deleted from your Rapid Rewards account balance. Southwest Airlines reserves the right to cancel the membership of any Member with no credits in the account and who has earned no credits for at least 12 consecutive months.
Maybe THAT explains the so-called "decent" availability. Take away credits you earned before you can use them EVEN if you are still actively flying on the airline. No thanks! I will stick with UA. I also prefer to fly in first class, something not even possible on SW.