Procreate
What else can you really say about this at this app is truly incredible.
What I love most about Procreate's is they do really prioritize how smoothly everything runs so the brushes all feel very responsive. The user interface is extremely clean although I will admit a lot of the more advanced features that really make you a power user are done through a lot of gestures, that can be somewhat tough to learn and understand however, it does have a lot of powerful features that can allow you to work very quickly if you utilize them.
Procreate's only works on an iPad. I would recommend an iPad Pro for this app mostly because of the larger screen but the developers do not want to develop this app to work on any other platform there so focus is the iPad this way they can make sure that they are getting the app to run as efficiently as possible on this one device instead of spreading their resources across trying to support multiple platforms.
A lot of people really love the app because it is not subscription-based you can buy at once, and never have to pay for it again, which is becoming increasingly rare these days. Procreate's has an amazing system for brushes that is pretty close to Photoshop and there is a thriving market online where artist including myself by and sell different brushes that people have made and they have it set up so it's actually quite easy to customize your own brushes, which is absolutely incredible incredible.
More recently, the app has been updated to allow you to paint directly onto a 3-D model, and with that their brushes now also include the ability to set up how those brushes are going to affect the different layers of a 3-D material, the roughness and the metal Ness of it can be set up in their new brush system as well.
One fun feature that Procreate's has is the ability to record a Time-lapse and I believe that setting is always on if you just at the end of your drawing, go to the settings and you'll be able to find an export a copy of it as a video, which is really cool to watch when you're done making your art art.
The developers have geared most of this app towards illustration, but it does work with many other forms of art.
If there's any artists out there, who's debating on what sort of art apps to get on your iPad? This is absolutely the first one. I would tell anyone to get… ever.