due to do 1 12 hour flight on an airbus - what is the best seat (ie: the most comfy / least traffic to the loo etc) obviously any near the doors would be best but those go pretty quickly to frequent flyers i guess?
There's no simple answer - there are at least 3 variants of the Airbus in regular airline use, and each of them can have a huge variety of seating configurations, depending as much as anything on whether it's a scheduled flight or a pack-em-in-tight charter.
you could look here, checking out your airline. Upgrades are pretty expensive but some airlines have a premium economy class, not too dear, that gives youvaluable extra space but without life-flat neds etc.