A350 would seem a better fit.Unlike the 777-200LR / -300ER you have a choice of engines.
A350-900 comes with GENX or RR Trent engines being developed for the 787,except they are not bleedless,and its family is being groomed as an A300/A343/767/777-200A replacement.
I hear the sales of A350 are not what they were hoping,so perhaps BA will get a good deal? A350 EIS is around 2010 when the 767s are due to be phased out,and the production slots are there for the taking.
I would place money on the A350
