I think it depends what you are looking for and when you are flying.

AMEX lounge is ok, with separate sections for Platinum (same as main lounge but fewer people) and Centurion (don't know what more you get).

AAdmirals lounge varies depending on what flights are departing. For BA flight there are wines and spirirts out. At other times of the day, it is coffee, soft drinks and maybe beer.

I'm not famaliar with the IB lounge, but I doubt it is better than their MAD flagship, which is hardly great.