I have an iPad Pro 12.9 inch , 3G... 1st gen ..
I use it for work ...I actually dislike my 2 Windows tablet (Helix 2 , Thinkpad 10)
It's great for note taking on the large screen
Split view is also great .
Excel , numbers , google sheets, - spreadsheet
Word , Pages , Google docs - word processor
Goodnotes - PDF , notes
The new ios11 should have productivity improvements
I still like the Surface 3 , charges via Micro USB , great screen , great battery life great sound
But since using IOS , I find it tends to be a better experience that windows .
I ALMOST ALWAYS need the pen and keyboard for Windows .
On iPad , I occasionally need the pen ... never needed a keyboard...stellar battery life is a plus .
And charging via a small power brick
So it tend to be Ipad for work , browsing web , movies , Windows for light games
Here are my suggestions
New Surface pro i5
Here are other worth mentioning
Transformer 3 pro
Elite X2 2017
10inches and above is great for productivity
Fanless is always beneficial
Small charging bricks are a plus
LTE is a must
Pen is a must