I'd hafta say Gintama. It revolves around Gintoki, a samurai who has defeated opponents that were seemingly impossible to defeat, like Saitama. I'd say that there's a lot of humor throughout the show. Gintama occasionally parodies other shonen anime. Granted, it's pretty slow at first, but a lot of the arcs are amazing. I got really immersed into the characters and plot. The anime started airing in 2006 and is currently ongoing. One of my favorite animes to date