We have both a Surface Pro and an iPad in my household. My wife uses the iPad for web browsing, Facebook, and online ordering. It is a terrific device for content consumption like she uses it for since it is simple, the battery lasts a long time, and it wakes from sleep almost instantly.
The Surface is better overall though. When it comes to writing documents, tracking finances, editing photos & videos, and basically doing productive work the Surface is a better choice. I've also got the dock that connects it to an external mouse, keyboard, and monitor so it can completely replace my separate desktop computer. Portable, powerful, and can sync all my files on-device using OneDrive, Dropbox, or another file service. It can do true multi-tasking and the Office integration between OneNote and other programs is wonderful. It truly is one device that can do everything. The only shortcomings are some menus in desktop applications can be hard to navigate due to scaling issues and the battery drains pretty quickly when it is sleeping.
The iPad is just too limiting even with the Pro split screen and pen. iOS makes the iPad more of a large phone which is becoming unnecessary as regular phones approach 6" screen size. I think the number of people willing to spend a significant amount of money on a second consumption device is getting smaller as phones get bigger. A tablet that can convert into a full-functioning computer is what customers are going to want.