Either would be a fine choice. I think the SP4 keyboard is also backlit.I decided to go with the Surface Book rather than the SP4.
Reasons for me:
- High-quality but still detachable keyboard / cover
- Keyboard backlighting
- Full size SD port
- Screen size
All I can say is, wow! The Surface Book announcement seems likes a direct response to my thread I almost pre-ordered but have some questions. I wish they followed up the conference with a more in depth technical discussion. Also, the SP4 seems to have a much better touchpad and keyboard, two of the things I was weary about with the SP3.