Having just gone through T3 again earlier this week (I try to avoid T3 and usually go through T5 when I'm heading to London, especially if connecting en route to elsewhere) and lounge-hopped, I can categorically say that unless you need access to noodles, or unless you are relatively claustrophiliac, the BA F lounge has a superior food offering and a far broader selection of alcoholic beverages, including the current Taittinger 2005 offering. Also there's an extensive selection of magazines and newspapers which you are encouraged to take.