This is a decent video comparing the two:

http://www.youtube.com/watch?v=Sfr508Dy6w8

It goes over the differences pretty thoroughly, and the rotation diagrams give you a good idea what you're going to be doing at 50. It doesn't go over what is more fun, but that's really because fun is more subjective.

General consensus is that MNK is the hardest dps to play optimally, but DRG can get pretty complicated too. I haven't played a DRG high, but I can say you'll have a better idea of how a MNK will feel at 30 (you get new form attacks at 26 and 30). However, you won't see the full picture until 50 when you get DK and perfect balance.