Moving this over from the Tag thread because my question has nothing to do with it: What are your favourite slime mangas? 
For me it’s:
In the “protagonist” category: Maybe predictably… 「マンガ」 転生したらスライムだった件 | L24. Action & battles? Check. Statecraft & economics? Check. A ton of fantasy races working together? Check. Not every single part of it is good, but the great parts easily overshadow those that aren’t. (I watched the anime though, I haven’t read the manga.)
In the “working with slimes” category: 神達に拾われた男 | L24??. The usual isekai setup - middle-aged business man is reborn into a fantasy world while being blessed by the gods - only to spend 3 years alone in a forest researching slimes. This one wins for me because it has some slime uses that I had never seen before, like e.g.
and has a nice balance between “slow life”, action and business. Absolutely recommended!
In the “enemy” category: RTA走者はゲーム世界から帰れない | L24??, featuring ラスピ, a slime that is one of the generals of the demon lord, which I enjoyed as refreshingly different to the usual “slime as newbie fodder enemy”. To be honest though, the manga itself is only so-so and I’m not sure I’d recommend it, but I don’t know any other manga with “big bad” slimes.
