I started with Sketchbook Pro. The program is good but very old. Sketchbook Pro is stuck in the past as the programmers spend more time on the mobile app. Please AutoDesk, work on Sketchbook Pro!
Up next is Corel Paint. Painter is a bad knock-off of Photoshop. I tried to like it but the interface was like sandpaper. I worked through the interface only to find it buggy as hell. Every day, every hour or so the prgram would crash. Corel promised the next patch would fix things. Thanks but I'll move on.
I found Artrage and loved it. It was everything Sketchbook Pro was supposed to be. Clean interface, guides, selections (try to select something in Sketchbook without moving it. You can't use selection as a paint border!) Artrage has become my tool of choice. The many blending tools are amazing. For all the blending tools alone is worth it.
One downfall of ArtRage is no perpective rulers. Hopefully in the next update it will.
Understand that this program is not Photoshop. It's not a photo editing program. This is a Sketch/Draw/Paint program. Because it's focused on Illustration it's better then photosohp. Have they added a color wheel to Photoshop yet? How's that canvas rotation? I'm sure in the next update they will get it right. For the price of renting Photoshop for a month or so you can own Artrage.