As I had meetings around LHR, I stayed at various hotels in the area but decided to try out other restaurants than the ones at the Sheratons and the Holiday Inns or Crowne Plaza, which I had the opportunity to try when I stayed there in the past.
I had a good experience at the Hilton, with both the Chinese restaurant and the (moderately) upscale restaurant (open for dinner only).
Two pretty good experiences, the upscale Brasserie at the Sofitel, which has an excellent wine list, with also a good selection by the glass. As in French restaurants, note that the
Filet Mignon involves pork, rather than beef

. Excellent starter and main course. Good cheese selection from France and Italy.
Another good experience, but in a somewhat lesser category, was the Tuscan restaurant at the Marriott (very practical for my stay at the Skyline). Very attentive service, good selection of wines by the bottle (not as good as the Sofitel's, of course), not so much by the glass. Food was far better than at the other hotels I mentioned earlier in my post. It was much better than the Olive restaurant that was in the past at the Skyline, but of course not as good as at the Italian restaurant in the FS Canary Wharf.
I will definitely come back to the Sofitel and the Marriott for lunch or dinner, even if I stay with my SPG, IHG and HHonors for my nights.