The conversion from the the B737-3/4/500 to the Airbus A320 took about two weeks in the classroom. (death by VACBI!)
Then about 2-3 weeks in the SIM, but that was in Toulouse and the French are not too keen to work weekends, so I daresay you could cut that down a fair bit if you wanted too.
Then 20 sectors to complete the conversion. As I was working for an outfit that did 4 sectors a day that didn't take too long.
I never flew the A330 but would have liked to.
I now fly an NG and have flown the BBJs as well.
My preference is for the A321. Nice flightdeck, uncluttered after the calssics, slightly faster than the NG and much quieter. All in all I found it very capable after the classics, an APU that was up to the job. Performance (at least on paper) was never a problem, that all said after 13 years on various versions of the 737, it is like a comfortable pair of old shoes, but I would go back to the 'bus in a heartbeat.