If you are serious about both drawing and writing, you're probably going to want 2 separate apps.
For drawing, the favorites are Procreate and Paper by FiftyThree. Procreate is a very full featured drawing app with all the bells and whistles meant for serious artists. Paper by FiftyThree is a very well-designed but much simpler app meant to recreate the experience of drawing on paper, meaning it has fewer features but the user experience is excellent.
For handwriting, the top 2 apps based on my research and personal use are GoodNotes and Notes Plus.
If your drawing isn't too artsy but more like doodling and illustrating your hand written notes, I'd recommend you Noteshelf as the one and only app you'd need for both drawing and writing.
Mainly because of it's extended tool palette where you can find pens, markers but also pencils. And they're all really good in giving you a realistic feeling.
Noteshelf is great. Definitely recommend it for both things.
I have Sketchbook Pro. It's not very good out of the box, you have to play with the pen/brush settings to get something you like. Paper is better in that regard, it just works better with a stylus compared to it. I've never used Procreate though as I'm very well invested into the Autodesk ecosystem.
I like Notes Plus too, I like that you can put it in fullscreen which is a huge advantage.