The freshly-made guacamole is worth the cost of the membership...

But to answer the question, it depends. I loved the Delta lounges when I flew Delta, but now I don't fly Delta. AA and United are the better options based on the geographic location. The Admirals Clubs tend to have showers more than othe clubs and so when I am returning from international travel the Admirals Club is a very good thing.

I love United's Polaris Lounges but find the floor staff the United Clubs to be rude.

If you fly AA a lot and have issues, the staff in the lounges can do so much more than the staff at the gate. 250 people in line at AA customer service and 5 people waiting in line at AA custome service in the lounge. I would pay for the lounge just to have access to the staff in the lounge if flying AA a lot.