Paint Shop Pro
I bought the first version for $29.95 about 7 years ago. It's usually only in that price range about once a year, around the time the new version comes out.
It's been an excellent painting/drawing application. Almost all the better applications of a type will do everything that all the others will do. They have to or they don't sell. PSP does everything I've ever wanted to do (fade fill, shaping lightning bolts, graphics overlays, etc etc) and done them easily.
Every one of them works each function very differently. In other words, common functions will be done differently. The idea is that you have to learn how each paint program draws a line, and every program will do it a different way. It's a real pain, but almost every computer application ever written tries to do everything their own "special" way. I guess they want to be unique. Or maybe they think we're too dumb to notice and will think theirs has something special others don't. About the only time one is less than another is when it's shareware or freeware that hasn't been developed much at all. Any application that's been around enough to be popular is going to do everything you expect or want to do.
I just created a set of decals for a model that's being refinished. I drew everything with PSP's drawing tools. In other words, I didn't simply scan and print (it's hard to fit a model aiplane into a scanner

) the individual decals. My set was actually "better" than the originals. I added rivets and shading to make some stuff more detailed and realistic looking. And it took me less than an hour to do. And anything, any decal, I can think up, I can do.
Any paint program will take awhile to learn if it's powerful. "Powerful" means full featured, and that means lots of things to learn. And all the popular paint programs are full featured.