Campagnolo EPS vs Shimano Di?
I'll declare an interest in that my company is the senior (Main) Technical, Service and Warranty Centre for Campagnolo in the UK - but having said that. the Service Centre work that we do for Campagnolo is not all of what we do - we supply general technical training to the industry across the board and I am also part owner and Technical Director of a business that looks after Services de Courses activity for races and spotifs here &amp; in Europe (www.servicecorps.eu), so I have seen the best and the worst of all the electronic and mechanical systems out there.

There are some urban myths around electronic - wet weather performance being one. This is not an issue for any of the systems in the market if they are properly installed. Shimano has slightly greater vulnerability because there are more breaks in the wiring loom than with Campagnolo but if it's assembled to Shimano specs this is not a problem.

Battery life - Di2 and Campagnolo are both around the same - both will give from a full 4 hour charge, something around 1200 km of normal use - it depends how much you shift and how the split is between F and R shifting. F shifting is more power consumptive in both systems. If the battery fails, Shimano defaults to the inside chainring. Campagnolo allows you to manually position the RD under any lower (easier) gear than the one you were in when the battery failed but you can't manually move the FD. In our experience, most people with electronic shift are so paranoid about this that in real life it's never a problem.

Electronic shift won't make you go any faster in and of itself ... it is more accurate though and once correctly installed, it will remain as accurate as it was the day it was installed, unless the user changes something, chain, cassette and chairing wear of course needing to be accounted for. The accuracy of shift remains, however tired the rider. In competition, this can matter.

Cost and cost of ownership - Shimano Ultegra Di2 is at a killer initial price point - the system is robust, spare parts are widely available and expertise likewise. Problems though, can be a headache to diagnose and the diagnostic software also requires (at the moment, anyway) connection through a relatively expensive interface to a PC. Campagnolo Chorus is comparatively expensive but offers a higher-spec, carbon crank set and on-board basic diagnostics. In my general (and genuine) experience, chainring and cassette life is better than Shimano, chain life can be better and I have never seen a correctly fitted Campagnolo chain fail - I have seen one or two instances with Shimano chain that I can't account for by fitting (but maintenance and use play into this and there is also a lot more Shimano "around" so that might also account for it on simple probability rules.

If the cost and availability issues are not the decision makers, then in terms of functionality, there is very little to choose - both shift, shift relaibly and well.

Some users prefer the ergonomics of one over the other, especially when wearing gloves - Campagnolo use a thumb lever to shift one way, a lever behind the brake lever to shift the other way so you are never in doubt which way you are going to shift - that's not always the case with Shimano with their closely-located shift buttons. Campagnolo place the feet closer together on all their crank designs than Shimano - this gives more options for bike fitting (if that is a consideration) and could be said to be inherently more "aero" FWIW.

Most of the choice, costs aside, are going to come down to aesthetics and ergonomics. There is very little bad product from Shimano or Campagnolo in the market now, design and execution from both makers is excellent. IME if SRAM could sort out some of their build-quality issues, they'd be up there as well but conversation with bike mechanics will tell you where their preferences lie and it's not as often with SRAM as with Shimano or Campagnolo - having said that a lot of mechanics are more wary of Campagnolo because they don't see it so often and equate doing things differently, with doing things worse. Not the case - but you do have to know how to set it up &amp; that's not the same was as Shimano.