The word from management was that unless you were already rated on the 747 or 777 you'd be going to the Airbus, but that was before they had to reopen recruitment and widen the offer (737 and 75/67 ratings now welcome).
As a junior FO on the 747 you could probably expect to get one decent trip a month to NRT,LAX,SFO,HKG,JNB,SEA,MEX as part of a blind line. The rest of your allocation will be JFK, BOS, MIA, DEL, MAA, ORD, BAH, IAD etc, mostly three day trips, plus you will work every weekend as a junior FO regardless of which fleet you're on. Bidding is really only a notional concept as a junior FO, you'll be on blind lines and be allocated your work regardless of your preferences.