I'm gonna go with Shinsuke from Sengoku Youko. It's another Satoshi Mizukami manga, but his progression from an optimistic, egotistic ronin to a spiteful warrior to a drunk dad is like the best thing ever.
The coach from Slam Dunk, probably one of the best mentor characters in manga. I like him a lot just like Iroh from ATLAB. Also, Sensei from Kakukaku Shikajika. He's so real.
Onizuka from GTO. Dude is one glorious bastard.
Munsu from Shin Angyo Onshi. Ruthless anti hero is quite fun to read, especially with a good backstory.
Eri from Fujimura-kun Mates. What's not to love about an emotionless, perverted, cloud-cuckoolander bishoujo?
Akari from Aqua/Aria. I can't think of another character who's more pleasant, charming, optimistic and sincere. She should be a saint.
Kumada from Oyaji. Probably the most genuinely badass character ever in a manga AND a fundamentally decent and sincere guy who really tries, albeit a bit too late, to be a good husband and good father.
I'm a sucker for badass and op characters:
Hei (Darker than Black), Yagami Ligh (Death Note), Alucard (Hellsing), Roy Mustang (Full Metal Alchemist), Shiba Tatsuya (Mahouka Koukou no Rettousei), Zwei (Phantom: Requiem for the Phantom), Emiya Kiritsugu (Fate/Zero), and Adolf Reinhardt (Terraformars) to name a few.
Hell, the only one I can think of right now is Alucard from Hellsing, cool bastard, but there are a bunch or even a lot of other good characters. Just a really cool character or rather an absolute monster. Also his 'background', his power and brutality.
E:
Heck, I love Lawrence and Horo from Spice and Wolf, their characters and the chemistry they have with each other. (Almost) A masterpiece.
The medicine seller from Mononoke (not princess) is kinda interesting, guess I am fond of Demon Hunters (I blame Warcraft, no, not WoW but Warcraft III). His 'character' and work...
Homura from (Puella Magi) Madoka Magica is badass and dedicated. How far would you go for your friends?
E2: I did not read the Mononoke Manga or any Madoka manga, just enjoyed the anime versions so...
Hmm... well Im more suited to liking couples intented characters, or misunderstood and underdog characters. On the back of my mind theres RELIFE's Arata Kaizaki/Chizuru Hishiro, Hiroshi Kido from Barakamon Ken Kitano from Sunken Rock. The Sket Dance trio and also the two otaku couples from Wotaku ni Koi wa Muzukashii
Xerxes/Kevin, I just love his entire character from the sad clown and how long he manages to hold on despite all the shit he's gone through and caused.
Hanyuu and the entire (main)cast of higurashi all deserve hugs.
Kumagawa the king of perverts is the first character to carry an entire series for me.