BA lounge at T5 is huge, has a buffet hot food area, dozens of wine and spirit options and large comfortable seats. BA lounge at Gatwick (South?) was muc smaller and didn't have hot food but was comfortable and plenty of soft and hard drinks. Servisair lounges on the other hand always seem to be small, packed and grotty with a choice of some biscuits and crisps for food (And signs saying you'll be charged if you take them out the lounge.
As already said the better lounges appear to be be those run by the airlines, the third party ones aren't worth it, unless you get them as a free perk with a card or affiliation.
Yeah the BA T5 lounge is pretty decent, was with my gf there once and she couldn't believe it was all free

