I have flown both types, personally preferring the airbus. I guess the main reason being the disappointment of the lack of advancement in the cockpit of the B777 from the B744, not counting the electronic checklist. The way I see the 777 is a great airplane held back by pilot design inputs.
Both types have shocking pilot seats and the 777 is very noisy in the cockpit.
Flying the 330 seemed to be a lesser workload especially about the equatorial regions as you had higher operational ceilings and could get above the weather.
The main reason that promped me to chane from A330 to B777 was the airline companies use of MFF (CCQ) and the effect it has on your roster when flying the airbus types.
Watch out SQ Airbus 345 drivers when you get the 330...