Can comment mostly on Atos.
Experience to be gained: They have a pretty well regarded FS team. People with a wide range of experience/expertise (KPMG legacy is an advantage) and they work with some big players on major projects - BP, ABN, etc...
Work life balance: Their managers are good and personable - your performance is generally measured on results rather than "face time". The atmosphere is friendly and relaxed, but very professional.
Remuneration: They will match any other firm out there, provided you have a track record to prove you can deliver.
As for PwC and PA: I know some PwCers, nice people, and they enjoy it there. I have worked with PA consultants: they seemed really technical and knowledgeable, but just lacked common sense, very nerd-like. But to be fair, maybe I have been unlucky and got stuck with a bad bunch. They are obviously good at what they do, they win enough awards dont they! Good luck with your choice. Personally, I would narrow it down to Atos or PwC.