For me my favorite Mangaka is Yoshihiro Togashi when he isn't playing Dragon's Quest..........
In all seriousness Togashi is the only Mangaka i have exprience multiple works of his Yu Yu Hakusho (only have seen the Anime though) and Hunter x Hunter. With Yu Yu Hakusho it helped set up a lot of stuff for modern day shounen and even does a lot of stuff better then series that was heavily influence by it cough Bleach cough. While art can get pretty bad( he does though redraw a lot of for the volumes and the art of the last 20 or so HxH chapters have been overall solid), his hiatuses make it very possible that HxH won't get an ending at all, and the final arc of Hakusho was very lackluster his story telling overall is incredible. A large part due to his villains cause i belive he is the best shounen Mangaka when comes to writing villains. Like while some villains like the bomber from hxh and the saint beast from Hakusho were forgettable. Togure and Sensui from Hakusho, and Meruem from HxH are some of the deepest, complex, and most well developed villains in all Shounen and quite possibly Anime and Manga as whole. (HxH Manga Spoiler) Plus i have a huge feeling Pariston and Beyond will be among them as well and Chrollo's character arc isn't done yet and there is a good chance Gyro will be a villain in a later arc.
He can also write solid romances like for example while childhood friend romance is a huge cliche in Anime and Manga Yusuke and Keiko is one of the best in the action shounen genre and only one i could think that is better from a seriesi have seen and that is between the main character and a love interest is Ed and Winry from FMA and it was interesting to see the main character and his love interest to star dating early on in the series as oppose to the end of it like every other action seires. Then there is Meruem and Komugi from HxH which might be the best romance in all Shouen and their death scene is hands down my favorite moment of the series
