Dissertations / Need to select a topic for my dissertation (economics) [2]

I am quickly approaching the time when I am required to select a topic for my dissertation (in the field of economics).

My question is rather basic: Is it better to select a topic that is currently popular - but that I am not very interested in, or a topic that I really love but may be much more obscure and problematic to research? I can see the benefits of both, but I don't know if I could maintain my focus for the length of time required for a dissertation on a topic that does not interest me.

Thanks,

Nick