Well, to start, here's an earlier post:
viewtopic.php?t=3008
As for my opinion, Kamiya's models get the most impressive award, with his Ancient Dragon, Bahamut, Wizard, the Phoenixes, and of course, Ryujin. I wouldn't say they are the most complex, but for sure, they are brilliantly designed. I know it might seem predictable that someone would shout out his name but nobody can deny his eye for detail and proportion.
I can't make a decision for Hojyo Takashi's models, but Lucifer is definitely a top choice. Utilizing the color change really makes that model stand out. And God of Thunder, Icarus, and others are also marvelous to look at. Sadly, I haven't folded many of his models, so I couldn't give a say as to how complex they are.
I guess I can't decide on the 'complex' or most 'time-consuming' designs, since I still have a limited knowledge of the origami library you could say. 'Time-consuming', to me, screams out modular or thousand-unit sculptures, but they aren't neccesararily complex.

I can't think of the names right now, but some of the gods of tesselation origami also have my respect, because for sure, they are complex, time consuming and brilliant.