Another vote for Di2 if it’s that or Dura Ace mechanal for the same price.
I’ve swapped out 6800 to 6870 on my road bike and like it so much I made the swap on my TT/Tri bike. That had Dura Ace 9000 and is now sporting a combo of R671/9071 shifters and 6870 derailleurs. I found the front derailleurs were finicky to setup for first gen 11 speed (6800 and 9000) and 2nd gen was better (R8000) but still not easy compared to 10 speed. Di2 simply made front shifting so much better.
If cost is an concern Ultegra mechanical is the best bang for buck over Dura Ace and a nice step up from 105 both weight and refinement wise.