I think at the moment the 777 is truly the best fleet to be on. They do do long flight and lots of hrs. So they get paid more overtime and hourly pay. Airbus is more relaxed and more days at home(Dubai).
Between 330 and 340 you have a good variety.
Upgrade is supposed to be the same time on both. Pretty fast on the 777, but with the arrival of the 380 next year, the movement should be very good on the Bus.
Get the job and then worry about it.