It's (of course) largely anecdotal but I've had better luck with SRAM (Force on Road and X.7/X.9 on MTB) than with Shimano. This is after owning a couple generations of Ultegra, LX, XT, etc. Easier to adjust, crisper feel, and lighter.
But that's subjective. Shimano makes nice stuff (as does Campy).
Not that what the peloton matters, exactly, but winning is still being done on mechanical groupsets. It ultimately comes down to feel, and not so much mechanical vs electronic. What gruppo do you like? Which one feels better to you? Do you like the feel of Campy over Shimano? Do you like the UX of DI2? Do you prefer the one lever SRAM setup? You need to ride some bikes and just get what feels better.
Of course electronic will get better. Mechanical probably will too. For my money, I'm waiting on a few things:
- As I said, I like SRAM better, I'd love to see the Chicago boys make an electronic gruppo. SRAM hoods/levers fit my hands better than Shimano or Campy.
- Better button feel. Shimanos buttons are poor affordances and still feel rubbery (remember Flight Deck). I've not ridden Campy's offering though. A more mechanical feel would be better.
- Better software. e-Tube (the Shimano "PC hookup") software only works on Windows. Fail. I only use OS X and Linux.
- Wireless. Is this possible? Yes. Right now I have my Garmin which can talk wirelessly to a powermeter. Until everything can use ANT+ and I can have one display to show gear/gain ratios as well as power, cadence, HR, etc, I'm not in a desperate rush. I'd think things are better now than when Mavic launched Mektronic...
There's an elegance to a mechanical group. I doubt mechanical groups will ever truly vanish (brakes wont be electronic anytime soon). They can only get better. There may be some future hybrid solution that beats all any way.
Long story short: get what feels right. Your group isn't going to be used forever. In 5 years you can revisit (if
you use it that long).