My sample size is definitely small, but I remember being particularly impressed by the brand-new AA Flagship lounge at MIA. I only got a fleeting moment to spend in it, but the decor was beautiful, the food selection was gorgeous, and the self service bar brilliant. Their salty chocolate chip cookies were very curious. There were a lot of people, but because of the size (also in terms of ceiling height, an often overlooked component), it didn't feel crowded.
Worst lounge (so far!) has been BA Club lounge in LHR T3. Packed like a doctor's waiting room, small, noisy and bit tattered. Corridor leading there looked like we were about to use a staff exit to visit a basement storage area. Not impressed with the food selection. We sat down for a single Baileys before making our escape back to the Qantas lounge for their scones and gin!