The way I see it is as follows:
747
Pros
Better destinations (Europe, American West Coast)
Not brand new, but still the biggest in the fleet and an all time classic
Cons
Most crew members will probably be based at the destinations, so probably not that much crew activities on trip.
777-300ER
Pros
Brand new aircraft with all the latest bells and whistles
Crew probably still mostly HK based, so maybe a party or two while on trip.
Cons
At the moment, not the best destinations.
Off course as the 777s become more, they will probably start doing more and more destinations.
The Johannesburg route is not that important to me at all. (Only a 24 hour stop over) which does not really give enough time to visit friends/family.
Oh well, maybe I should flip a coin...