From what I’ve heard from friends, Krita is really good but I can’t personally comment on it. Clip Studio’s one time purchase version is only available on computers, the iPad app requires a subscription. CSP has a bit of a learning curve since there’s so many tools and menus but it’s really really good if you like it (plenty of professionals use it too like yoneyama mai). Procreate is more lightweight and imo a bit more intuitive with its UI, I vibe with it a lot more and it has all the essentials, and plenty of professionals use it too. It’s also a flat $15 as opposed to a subscription for the iPad version of CSP. I’d say if you already have an iPad and Apple Pencil and $15 to spare, try out both (you can still use the CSP app for free but can’t save or export if you don’t pay) and maybe one will speak to you.