I heartily believe all of the positive press about electronic shifting (fast, effortless shifts, easy set-up, a cleaner look, etc.).
However...
In my 35 years of cycling, properly adjusted mechanical drivetrains have never let me down, and mechanical shifting is not appreciably slower. If a chain is acting a little chunky going up or down (a rare event), 99% of the time a quarter or half turn of a barrel adjuster does the trick. What I gain by sticking with mechanical shifting is never having to think about batteries (When did I last charge this? Do I have enough juice for the ride I'm about to do? If my battery dies, how many miles will I have to limp home? What will happen to this battery when my Northern California garage hits 130-140 degrees in the summer? How is it that Pro Tour riders, who have team mechanics, need bike swaps mid-race because their e-shifting isn't working?).
None of this is meant to be a criticism of electronic shifting. The people I know who use it love it. Excellent! But mechanical shifting is so simple, reliable, and effortless, that for me, e-shifting is what I call "a solution looking for a problem." My main sadness is that Shimano and SRAM only offer their 12-speed kits in e-form, forcing me to choose between that added gear and peace of mind.