There is so much to choose from. It really goes by the readers personally preference. I would read any BL manga depending on my mood and what I fancy to read. I brought a range of mangas to read. (It’s like creating my own mini BL library at home)
There only a few manga books I would Constantly read.
Here are my top recommendation:
1. Junjo Romantica; By Shungiku Nakamura. great romantic storyline combined with hot smutt. A romantic story between a wealthy man and young student. You can read it for free on MangaFox.
2. Strange and Mystifying Story vol 1 and 2; by Tsuta Suzuki. A handsome mysterious demon with wolf ears cures an illness of a lonely young man. Beautifully drawing style and great romance.
3. Crimson Spell; by Ayano Yamane. fantasy action with lust. A love affair between a mage and Prince. The prince is cursed and turns into a demon at night. The Manga can only tame the demon by giving the prince sexual release. Absolute guilty pleasure!
This list can change anytime. I do have more BL manga book to share.