I think you've all made valid points on the two parts. I must say that something similar to the first film has happened (more than once) to me, and I feel it's a very realistic and romantic film. But I must say, that the second one appealed much more to me, as the characters are closer to myself (though I was still a bit complaining about their immaturity to myself during the screening, but probably I saw myself in it more than I wanted ) It is difficult to do the right thing in reality, though we often know what we want when alone...
I also think it has to do with your own experiences which one you prefer, and while I'm 22, that doesn't have much to say in itself. I think the second one is even more romantic and idealistic than the first film, exactly because of the many disillusions the two characters have gone through - and still they are trying to find each other again. In the first one both were more in the way of finding themselves and exploring the world for the first time, which is what most people go through. But after some disappointments many settle for something in the middle and become more "realistic"... 
I always try to feel enthusiasm and passion anew, and try to see my past mistakes more like something to learn from and improve upon. 
But I'm still waiting for the third which i hope to be final perfection (though I don't know how it could develop, as my personal experience sadly hasn't undergone such reunitements )