I read tons of manga and there's a lot of gold to be found. However, considering you and what you like, I can recommend without a single doubt in my mind anything written by Naoki Urasawa, who is the writer behind Pluto, 20 Century Boys, and Monster. The man knows how to write tons of great and complex characters and tons upon tons of plot threads and bring them all together in a very satisfying way without leaving anything loose threads. Monster is hard to come by sadly, but 20th Century Boys is easy and is a must read.
I started the Monster anime; so freaking good. Thanks for the suggestion.