Definitely Broadway cast hands down. Maria Friedman's Fosca is so hammy that she turns in what I see as a pretty embarrassing performance, at least on the recording. She's just atrocious. She goes for big and in doing so misses all of the nuances and complexities that Murphy so brilliantly brought to the role.
Donna Murphy's performance in the recording is worth getting it alone, but Marin Mazzie (who's performance as Clara is as definitive as Murphy's Fosca), Gregg Edelman and Jere Shea are great in the Broadway recording too. Yes, the London recording is more complete, but when you have a Fosca that comes off as more laughable than tragic, the whole thing falls apart.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"