Gerwin said, what I would have mentioned. maybe we should really add some information about WHY we like that specific designer so much. there is more then one reason to like somebody
I don't give an order, but tell you this:
I like John Montroll very much, because most of his models are really fun to fold. ok, compared to the modern high-tech-designers like Kamiya and Co the models looks somehow clumsy but maybe realism isn't really the most important thing.
I really adore Komatsu, because (like Gerwin mentioned before) his models seem to fold themselves. you always need to do a billion precreases, but in the end, I always appreciate it.
Eric Joisel gave Origami a new face, I think. he pushed it more in the art-direction. I like that, and he's models are very unique and always wonderfull.
Like Joisel, I also think, that Vincent Floderer brought something new into origami: don't fold, just crumple. creating another elephant wouldn't be too creative, but creating a new technique is something special.
I love David Brills Models, because he also has his own folding style. he always tries to get most out of the paper, without hiding too much within the model. he's models are very nice and 3dimensional. because of that, I would also mention Stephan Weber here...
maybe somebody that is doing more modular stuff should give an answer