In a french frenzy I revisited both these places over the course of two days last week. La Poule au Pot in Pimlico for lunch and la Trouvaille for dinner.
Both are similar as La Trouvaille is a break away/copy pf the alma mater in Pimlico. I have to say that I was disappointed for the second time in a row with La T, with shoddy cooking, starter served burnt, main course served cold and a 50 minute gap between the two.
The old school Poule au Pot was right on form, with the joi de vie, friendliness and skill of the service, the ancient, eccentric room(s) and some superb cooking a la grand mere. An astonishingly good hunk of tart, perfect liver and a creme brule to finish and, of course vast quantities of wine.
Right now if I was recommending between the two, it would be La Poule au Pot every time.