Gunma, cause I love the girls and how he draws breasts.
Yamatogawa, overall simple storylines and all around great artwork, most of his works are barely censored to begin with, so they usually get completely decensored in time.
Cuvie, mostly for the incest stuff :3 Also, his works are generally uncensored.
Ishikei, the god of full color doujins. No one comes close to his epicness. Weather he draws lolis or big breasted sisters/MILFS, his stuff is just faptastic.
Nekomataya, that artist has made easily the sexiest and hottest Sakura (from Naruto) ever. Easily. And those are some of my personal favorites from him. I also like how he draws breasts, they always look real succulent :3
Hikakuteki Simple na Panty. Two words: Harem doujins. Nuff said. :D
Mitarashi Club, they've drawn the hottest MILF ever IMO, Akiko Minase. They draw superb drawings and the Kanon parody's with Akiko-san are some of the best doujins I've read. I love how they built up the tension for the sex scenes, AND NONE OF THEM HAVE DISAPPOINTED ME SO FAR. :D
Gorgeous Takarada, no way near the best artwork, if I had to say it's average. But what makes up for it, are the sex scenes and dialogue, SO HOT!!~
Tanaka Ekisu, since most of his works involve incest. So for me, that is instant win. :D Also, this artist draws some reasonable size breasts, by that I mean I've never seen him draw beyond C cups, so maybe for those that are interested int that could like him too.
Kensoh Ogawa, big breasts specialist lol. Not too big for my tastes, and I just love his artstyle. Plus, the honeyblonde series was pretty damn awesome, not the best thing I read, but there was plenty of variety in the sex scenes and the locations of those sex scenes. Also, his girlfriend lactates when they have sex, that's hot.
Bosshi, well what easily comes to mind is "Mizugi Kanojoe", easily the best doujin-to-movie adaptation I've ever seen. The artwork in the movie is just faptastic, delicious breasts and real nice nipples. As for the doujin books, I think I like 95% of his stuff, just found the doujin about the guy that goes to the gym and has sex with the girl staring at him retarded, the story was just...ridiculous. But the artwork is always awesome.
Hellabuna, for making great parody's of various video game babes (DOA's Ayane and Kasumi) as well as animes (to-love-ru for example). The artist usually draws some clean, hairless pussies, good for a change and for those who prefer that. Breasts are usually drawn in D-cup size too, nice titfucks and usually draws the inside of the pussy when they come, and I love it when artist do that. :3
Last one that comes to mind at the moment is Studio Wallaby, I don't usually like all their releases, but the parody's they made of to-love-ru were freaking awesome. My 2 favorites are "To Love-Ru - Trouble Musume ~Haruna & Ryouko~" and "Trouble Musume Haruna and Yui". Breasts are pretty much average in terms of drawing quality, no way near my favorites like Gunma and Nekomataya, but I LOVE the fact that in those 2 doujins, they keep their panties on and push them to the side and fuck with the panties still on. There aren't enough doujins where this happens IMO. =(