OK, this has probably been debated to death, but I'm curious.

When I was a "Player" in the 80's and 90's I was always a member of an airline club program so I could enjoy some peace and quiet in busy terminals during long layovers. I was a member of TWA (can't remember the name of their clubs then), American West (can't remember that one either), and American's Admirals. I also dabbled in the Red Carpet on United, and Delta's Sky Club.
Last fall I bought a 30 day at Delta's Sky Club. Not sure I got my money's worth for that 30 days.
The past 10 years I have been flying on-the-cheap for the most part, and of course there is no clubs on Southwest or Airtran.

Those that fly the majors, what is your favorite club and why?
Do you think the club cost is worth the investment? How much to you think you have to fly to get your investment back?
How would you rate them on amenities, service, and comfort level?

Thanks!