I say its better to have one good laptop than a macbook and an imac because you would have to keep them both in sync, where as if you had one laptop you can just pick it up and take everything with you with out having to faf around with file transfers.

Im using my macbook pro as my main computer as a desktop at home then a laptop when im out and about and its much easier and more practical han when i used to have a seperate desktop and laptop.