In the embedded video, Serenity Caldwell used the iPad Pro and the Surface Book (same screen as the Surface Pro 4) to do some similar sketching tasks using built in tools, all with informative running commentary.
Later in the video, Serenity switches the Surface Book to desktop mode and uses the tablet to draw with the Photoshop. Next, she moves to the iPad Pro, using Photoshop’s iOS tools (pieces of the full Photoshop, all designed to create content, which you then share using Creative Cloud).
To my untrained eye, the iPad Pro seems much more responsive, the Apple Pencil more precise. As you watch the video, watch as Serenity pinches to shrink her drawings. The iPad Pro seems to respond immediately, while the Surface Book seems to do a bit of thinking first. This could be the video, but it does seem consistent throughout the video. And, of course, Serenity’s comments about the precision of the Surface stylus support this notion.
On the other hand, consider that the Surface Book has access to the full version of Photoshop, while the iPad Pro uses lighter weight apps specifically designed for iOS, all designed to share back to the cloud and/or your Mac.