I love most doujin circles.
Probably the most emotional was Aozora-Market's "Scarlet & Scarlet" doujin. Espcecially when Flandre found out that Marisa's dead.
All of Hole of Yago's works are amusing in it's own chibi way.
FLIPFLOPs doujin are usually good. The PCB and EoSD re-interpretations were great, and the seasonal doujin are always quite hilarious. Also awaiting the Autumn doujin as well.
Millet Soup is probably the first doujin circle I read doujin from. It was called "Well-Ventilated Workplace". Funny doujin. As well as the Flandre one. Currently the third doujin concerning Cirno is being scanlated. I'm awaiting the final release.
Hole of Yago...ah yes, this group. I love their Yakumo/Moriya doujin. I guess now it's moving on to the Komeiji family and their hilarious antics. That means more Koishi~
ReverseNoise is probably the best artist out there for me. Both of the H-doujin and SFW doujin are good. They're usually quite hilarious.
Takaku-ya's h-doujin are usually quite hilarious, while still keeping the material very fappable. Touhou Enchantress Dance 9 was awesome (lol Iku's shock-orgasm with Tenshi
).
I could go on with the huge list of doujin circles I'm definitely into. There's just way too many to do so.