I'm currently using a combination of a Wacom Intuos5 and a 2010 iMac, and my favorite software is definitely Photoshop. Needless to say, though, I don't do a lot of digital art on the go.
While I'm always gonna be pro-apple for just about anything, if you want something mobile with as much versatility AND the ability to support some of the more common art programs than the Surface might be the way to go. However, if you're intent on an iMac and an apple pencil (really though? why's a stylus so expensive?) I DO know of a few similar programs that operate on the iPad. How well, though, I have no idea.
While I'm always gonna be pro-apple for just about anything, if you want something mobile with as much versatility AND the ability to support some of the more common art programs than the Surface might be the way to go. However, if you're intent on an iMac and an apple pencil (really though? why's a stylus so expensive?) I DO know of a few similar programs that operate on the iPad. How well, though, I have no idea.