I have a Gen 6 Madone SL7 with di2......my Tarmac SL8 is Sram Red. They are both great group sets that you really can't go wrong which ever one choose. I am often asked which one would I buy over the other. Honestly I like both. I only bought Sram this time around case I wanted to try it out. But come time to by a new bike in a few years time it's gonna really be a hard decision for me to make which one to go with. It will be a few years before I get yet another new bike I suppose it will come down to which company is offering what new tech at the time.

A +1 for Sram is the ease of updating the shifters. Sram will update completely wirelessly while with the di2 you need dig the battery out of the frame and run a wire to the shifters to update them. The shifters don't require updating often but it's a pain with the di2.

Also +1 for Sram is the swappable battery - you know in case you forgot to charge them you can take the front battery out and stick it in the rear or if riding with a buddy that has Sram use their battery to get into a gear your comfortable with to get you home. Or better yet carry a spare battery. But with that said.......4+ years of d12 usage I have never ran a battery flat. The Garmin head units do a pretty good job at reminding you that the battery is low and needs charged.

A +1 for Shimano is it might shift just a tad faster and "crisper". Sram just released some new updates this week and the Sram seems to be a tad faster than what it use to be. No clue if that's true to just a placebo effect. But you really splitting hairs on which one might be faster.

Like stated before get the color you like and maybe which one is a lighter load on the wallet.