I've had DA Di2 on one bike for 7 months, and Ultegra Di2 on another for about a month. Functionally they are identical. The only difference I've noticed is that the servo on the FD on the Ultegra version makes a little bit different "zzzzt" sound when it shifts.

I have the wrong cable kit on the UDi2 bike. I need to get that fixed. The cables are too long and they wrap funny on the bike. On the DA bike the cables are held to the frame with heat shrink tape. Nice and clean (for external cabling anyway.) On the Ui2 bike the cables flap around and are only held on with zip ties. I get lots of "cable slap" noise. I'm going to remedy those things shortly.

Other than that unless you are seriously concerned about the weight difference, I don't see any reason to go with the DA version at this point.