I have been in ZRH Kloten, and in LHR, and also in Frankfurt-Main Airport (FRA)
I would say I liked all of them. Moreover, since I am Greek , I've been in most of the Greek airports.
LHR, has indeed a lot of variety, but also very easy transportation means both within, and also for London.
Zurich Kloten, is very good to wait, cosy but not congested, with great views to the runways. Also the view overall is one of the best.
As far as the Greek Airports are concerned, I would say that they lack the organization of the big international airports, but during big stopover, I have many more options there
Also check out the Greek Duty Free Shops. Great deals.