I belong to 3 ----- WN
's Rapid Rewards, AAdvantage, and CO
Of the 3 I prefer Southwest's far and away.
It depends on what you want to do with your miles/credits.
If you wanted to vacation in Tierra Del Fuego or Tanzania, Rapid Rewards would not work.
If you are okay with being able to go places within the continental United States with a minimum of fuss or restrictions, Rapid Rewards puts all others to shame.
Every time I hit the 16th credit, they mail a ticket to my house. I get it out of the mailbox and put it on the mantle. Whenever I want to go someplace, I call and book a reservation. A very few blackout dates annually (usually around 4th of July, Labor Day, TGiving, XMas). If there is a seat on the plane, I get it. There are no capacity controls on Rapid Rewards rickets.
From out here in El Paso, the tickets are really nice for going to DC or NYC.
Right now there are 3 tickets on the mantle and another in the mail.....I passed 16 credits yesterday and have 3 1/2 towards another ticket.