As someone in the small minority who did both English Lit and Chemistry, I loved both so I think it really depends on personal preference. Chemistry is a hard A-level but generally due to having to apply your knowledge in unfamiliar contexts and the difficulty of the concepts you have to learn. It does require more frequent revision than English Lit in my experience, but it's easier to revise because you can just do past questions. If you enjoy problem solving then Chemistry will probably be a good fit for you.
English Lit is also hard but generally due to the sheer volume of content that you have to do and the memorising that goes into it, even if your exams are open book. Comparatively, there isn't that much memorising in Chemistry. I also think that doing a humanity complements STEM subjects really well as it gave me a proper break from my other two subjects (Chem and Maths) and I feel more well-rounded as a person. The enjoyability of English Lit does depend on the texts you're studying, though, so it might be worth seeing if you can find these out beforehand to assist your decision.
That being said, there is lots of overlap in the skills needed. You do still have to apply your skills in unfamiliar contexts in English Lit via unseen poetry and you do have to memorise certain things in Chemistry (like mechanisms). Controversial opinion, I think if you're suited to one, you're suited to them both as they're both analytical subjects at heart.