I recommend you test ride both, and choose which you like better. You may find the electronic shifting to be awesome in operation, so you spend the extra money and deal with the associated complexities (weight, battery life, obsolesence). Or, you may find that they operate about the same, and you'd be happy with the mechanical group and more money in your pocket for other upgrades.

I mentioned obsolescence because a mechanical group can always be supported and repaired, so long as you have the correct (or equivalent) parts. An electronic system will eventually be non-supported by the manufacturer, so you won't be able to get new firmware support. Compatible parts are much more specific for electronic groups, and you may not find compatible parts in the future because there won't be third-party offerings.

A new bike with either group is a serious investment.

Personally, i'm not much of a roadie (I prefer gravel and dirt), so my new component purchase would be the RS-685 hydraulic disc brake/mechanical shifting controls. Shimano makes a Di2/hydraulic version (RS-785), FYI. I just don't think that Di2 offers much value for the added cost/complexity (in my opinion, according to my riding style and self-maintenance)