I had a couple of nightmare journeys on BA due to the seatpitch. The first was LAX-LHR and although I was only 14 at the item I felt like a sardine. Three years later I flew CGK-KUL-LHR. Ok so being 6'3 didn't help on the latter flight but it's a very long flight when it's dark all the way for 17 hours and you don't get any sleep.
Both flights were on 744s. However the BA 734s and 757s are much more comfortable in economy.
The worst seatpitch I ever experienced was this summer on a JMC 757. But then again you don't expect legroom on a charter flight!