If you will be flying Economy Comfort I would chose the A330-300 and try to get seats 10AB or 10HJ. As many have commented on FlyerTalk, those seats are great for long-haul flights. Economy Comfort on the A330-200 starts at a bulkhead wall which I don't find comfortable.
For regular coach class (not EC), there isn't much difference between the two except the number of passengers.
I can't comment on Business Class for either aircraft.