Mine would also be aux tracks and patch points, but they were 10/2015.
 
And it would be load balancing, but for the only project where I had problems with high CPU load in one thread, it didn't help. It looks better balanced, but the drop outs persist. (Changing power management helped.)
 
So, it's smart swipe. Really nice to show/hide lots of tracks in PRV at once.
 
Here's my list of major changes for 2016:
2016.11: Lenses, WASAPI drivers, Matrix View Enhancements, Browser (Notes Tab, Synth Rack)
2016.10: Softube’s Console 1 support
2016.09: Plug-In Load Balancing
2016.08: Plug-in Browser Enhancements, Take Management & Comping Enhancements
2016.07: SONAR Theme Editor
2016.06: Smart Swipe Track Controls
2016.05: GUI Theme Selection, Tungsten Theme
2016.04: LP EQ and MB, TH3 Cakewalk Edition
2016.03: Melodyne Tempo Detection, Help Module, Ultra Analog Session 2
2016.02: Add Track Menu, LANDR
2016.01: Melodyne 4 Essential

Oh without a doubt, the best feature since the pc could record and playback multitrack audio, was tempo extraction from free form audio. - Thank you. This is liberating for me.
 
Themes are cool too.
Oh and Fx Load balancing.
 
 
 

What. No love for the add track button?

Definitely Smart Swipe.

For me it's the Tungsten theme and the load balancing. 

Load balancing... It's been amazing!

bitman
What. No love for the add track button?

None, I thought the main purpose was to help beginners. For Midi I still prefer insert soft synth as simple instrument track. Seems quicker

TPayton
Tungsten theme.

+1 
 
The only reason I bought it. Well ok, it was lifetime updates that sealed the deal, but the dark theme is the only current feature that actually made me want to have it.

My favorite(s) has to be Smart Swipe, Console1 support and Tungsten theme among others 
All the best.

Load balancing, without a doubt. Many physical modeling plug-in presets from companies such as Arturia and AAS, which previously stuttered badly on my not so top-notch computer, are suddenly possible to use.