You're saying it like you will have a choice...
Not many more SO courses for the 400 these days. But to answer your question.
Pro 747: Good rest to EU with mostly based crews and everyone working on their body clocks.
Cons 747: The oldschool longsleevers are still here.
Pro 777: Fleet of choice (at the moment) good choice of destinations/layovers
Con 777: The oldschool longsleevers from the 400 are 'ticking the 777 box' before retirement.
Con 777 (all fleets): Terrible crew hotels.