I would say it depends a lot on what you like. I have done a lot of both and they both have positives and negatives. With Domestic flying you tend to stay near your home time zone, if not entirely within it. With International you can very easily go 12 times zones out. That takes a big toll on the body, especially the longer you do it. With International you also tend to be away from your home and family for longer periods of time. If you have young children at home that puts a strain on your marriage and stress on you for missing your kids events. My wife absolutely forbids me from flying the 11 day Melbourne trip and when our son is born I won't want to do it either.
As profile says, the variety of International can be very interesting and helps to keep things fresh. When I get tired of going to Asia, I'll bid Europe trips. When I get tired of Europe, I'll try to do trips to Africa and around the Middle East. The layovers tend to be longer as well, we have very few layovers less than 24 hours and many up in the 48 and 72 hour range. It is a good way to explore the world.
It would be nice if the U.S. airlines did aircraft bidding like some of the European airlines. Pay by seniority only. At places that do that it tends to be the younger guys who bid for International and the older ones who stay domestic. Unfortunately, in the U.S. you have to fly International as you get older to maximize your income and retirement.
Typhoonpilot