I'm going to throw a whole mix of different genres so bear with me:

Grand Blue
(The funniest manga I've ever read)

Vagabond
It's a gem of a manga

Kingdom
Has amongst the best arcs in all of manga (cough Coalition arc cough)

These two are probably the most underrated psychological thrillers I know about (Shinobu Kaitani is a genius);
Liar Game
One Outs

Edit: You should also check this manga out in case you like ONE and his style:

MASHLE

Also this masterpiece:
Vinland Saga