If I could only choose one, I'd definitely go with the 950XL. I'm a business owner so a bigger screen, faster processor and bigger battery would all play a role in allowing me to be more efficient on the go. I would also get the display dock to connect to have a second PC handy rather than having my intern bring their own laptop, and an octa-core processor would ensure I never slow down.
I would not, however, complain if a 950 was my only option. It still has functionality that is unprecedented in a phone. These phones are friggin awesome!