I have to go with the Diaz brothers at the moment. Frankie Edgar is good, but a lot of what he does is based on his athletic gifts. The Diaz brothers aren't blessed with Edgar's speed. They're still good in spite of this. The Diaz brothers put punches together better than anyone I've seen in mma, and include good body work in their attack. They also understand the punching range better than almost anyone I've seen in mma. Wanderlei is a good striker overall, but he doesn't belong on this list. When it comes to hands, it's almost like he closes his eyes and just starts swinging.
Mousasi is a good shout. I think he is physically weaker than most of the top fighters at 205, and is only good because of his technique.