Hi I am new to cycling and thinking to change my groupset Ultegra to either 6870 di2 or Dura ace 9000 can get either for around the same sort of outlay I only cycle for fun and exercise can some one give me any ideas or preference for either item bike is 2015 Dogma think 2 Thanks
DI2 is an electronic shifter. This is not really necessary for fun or exercise, a good old cable groupset will do. I always use old shifter sets that work simply because I don't race. I'd buy something cheaper than the Dura-Ace 9k, I'd go for Shimano 105, I personally find they feel exactly the same other than really slight mechanical habits such as feeling slightly looser than the Dura-Ace, but that's negligible compared to the price and the value out of it.
If anything, stick with a cheaper groupset, you won't need the other fancier ones.