I think it is definitely better to be the bigger person. Not only does it make for a smoother transition, but in the long run I think it helps you not to dwell on things if you haven't over-reacted about them.
I haven't been the most adult in the past when a relationship ended. In my last one though I am happy to say I made it very easy for him. I was kind and understanding and I didn't pout about it. There are still a lot of unanswered questions for me but I try to tell myself that it just wasn't meant to be and I have a future in store with someone even better who will love me forever and not break all their promises.
It's always better to look ahead, not behind you.