Another difficult choice, well…my favorite so far is Sangen Tonari no Tooi Hito but Merry Checker seems like it’s going to take the spot soon.
You could barely consider this a BL, since it feels more like Mitsuya’s story; it’s about his daily life and the reasons why he is a bundle of stagnant feelings in spite of his cold exterior. What I like the most of this is how the story is told, from Mitsuya’s point of view, in a way that makes you feel like you are in his shoes. Maybe this happens to me because I can identify with Mitsuya in a lot of areas, specially his bluntness and practical (much) view of life. I wrote an extensive review about this manga for the club too, where I explain why I think it is so good.