Well personally I would prefer it if not everyone would achieve his goal at the same time. OK of course everyone´s dream should be fullfilled towards the end of the series but in terms of writing a climatic story you have to give people some of what they want already but at the same time leaving them anticipating for the big bang.
And btw I think it would be even more proof of friendship if people would stick with Luffy, helping him to achieve his goal after he was always there to help them reaching their dreams. This would also be great because it would mean that they not only would love to achieve their dreams, but also that they would want to do it together.
The way how I see it there´s three groups Straw Hats when it get about when their dreams will be fullfilled. I think that Usop, Sanji and Zoro will be the guys who will be first to achieve their goals.
Afterwards Luffy and Robin would get what they have been searching for since I think that the true history and the One Piece are linked to each other (but they´re not the same).
The third group would be Nami and Chopper who I still see living on continuing what they do. Actually no matter what carpenter will join, he would also be in this group since he´s dream would be to build a ship that can travel around the entire world. So he´ll keep with his nakama and the ship until the end (you know who I`m reffering to, don´t ya?).