There are four clubs at ORD. (or five, if you count the INTL First Lounge, which mere mortals never get to see.)

2 on the B concourse. The one down by the lower-numbered gates is upstairs and feels big and cold. It can get busy at times, but I've always found a seat. The one at the other end is also used as the LH lounge by default since it's very close to the gates they use. This is the "new" lounge and I like it although it can get busy prior to LH flights. It's a huge improvement over the old lounge that was in more or less the same location and didn't even have its own restrooms.

1 on the C concourse. This is quite large, and can get very hectic when the INTL flights are departing. I like the part by the windows where you can sit at little tables, most of which have power available. Better for me to work at a table instead of from a lounge chair.

All three of the B/C clubs are similarly stocked with [bad] food.

The current F lounge is a pit. Nothing more to say - small, tight and overcrowded. But, the new one should open soon and I'm crossing my fingers.

All four are inside the same controlled area, and during a 12 hour stay at ORD (don't ask) I wandered into all of them, but in all honestly I just pick whichever one is closest to my departure gate.