Wich yaoi manga that no matter how many times you read you still enjoy it? I know how much...

Yami no kodou

Monster petite panick, Puchitto hajiketa

Anything by Naono Bohra! I can't pick a specific one because once I read one I go on a reading spree and end up re-re-re-reading them all. ╮(￣▽￣)╭ (๑•ㅂ•)و✧

I always come back to read this, http://www.mangago.zone/read-manga/puchitto_hajiketa/ every once in a while because I love how the seme is super sweet and never very forceful with the uke. You can also see that the seme truly cherishes the uke too and I love that.

And these are other favorites of mine:
http://www.mangago.zone/read-manga/kyoushi_mo_iroiro_aruwakede/
http://www.mangago.zone/read-manga/follow/ (uncensored penis' :v)
http://www.mangago.zone/read-manga/kawaii_akuma/
http://www.mangago.zone/read-manga/canis/

Any of the Kuroneko Kareshi one's they're just amazing

Merry Checker, Yume no kodomo, anything by Naono Bohra… mhhh you could just check out the first 3 pages of my favorites list… http://www.mangago.zone/home/mangalist/40317/?filter=&page=1

Puchitto Hajiketa is seconded, and also Kami-sama No Iutoori and Punch up

http://www.mangago.zone/read-manga/junketsu_drop/
love this ish

Aitsu no Daihonmei and Muchuu Hito <3

Shounen Ai: Yozora no Sumikko De
Yaoi: Doushiyoumo Nai Keredo (with all the extras and the after stories)