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.