So, the Surface Pro and Surface Book are interesting products. And I think the engineers behind them did a lot of good work. But they both (to me) make a particular statement that isn't quite what I'm looking for. And that statement is "I want to replace your laptop with Laptop Lite".
The Surface Book seems great when you mostly need a laptop, and sometimes just want to use it on the couch. Definitely a use case there. It also has a premium price tag to boot, being 200$ more than a similarly spec'd MBP 13". And you have to shed the keyboard to get down in the ballpark of the iPad Pro in terms of weight (something folks are criticizing for being too heavy). For those that want it, great.
The Surface Pro tries to be more of a drawing tablet, which is more up my alley. Still a hair on the heavy side compared to the iPad Pro. And price competitive to boot. If I bought either, it'd be this one.
The catch there though is that honestly, Win10's convergence approach means that many apps will basically do the bare minimum (if that) to support something like the Surface and move on. So while it could, in time, conceivably be a tablet that makes a good tablet, it is totally up to 3rd party devs, and running the Windows desktop just means that you aren't in any hurry to adopt the new UI when not docked. On iOS, you are either there with a tablet-first app, or not at all.
EDIT: And the Surface Book is only good for 3 hours without the keyboard. Yikes. Not something you can use mostly as a tablet at all.