I personally like Kisaragi Gunma because his artwork and storylines are really good his girls don't ever get plain for me. I really liked what he did with the Love Selection series as well as Mai Favorite and Giri Giri Sisters. All doujins wind up into some kind of sex frenzy, so don't think that Yamatogawa is any different. He does a fantastic job as well, my favorite of his was the Tayu Tayu series, but his artwork I find to be a little different from my tastes. Although he makes up for it by giving the girls a personality and gives his work a bit of realism. For Gunma's artwork of course you'll see a repetitiveness, but that's probably because he has made more doujins than Yamato has. But of course I don't really know much about either artist I'm just saying all this as I go from looking at all the doujins that I have, so Kisaragi Gunma FTW! =P