As far as shifting goes electronic rear derailleurs need the cassette ramps just like mechanical. I guess they can push the derailleur down as well, whereas mechanical relies on a spring (and it's weakest going into the smallest cog). However the ramps are good, the upper pulley is close to the cogs, so a mechanical rear works really well.
For the front there's no beating electronic. The acid test is going into a steep hill in the big ring and then shifting into the small ring as you run out of momentum. With a mechanical derailleur you'll fail that shift pretty frequently as the spring isn't strong enough to overcome the chain tension you create by desperately pushing the pedals so you don't fall over. It helps to have the lopped off teeth but it's pretty normal for the derailleur to simply fail to move over. With electronic that was the selling point they presented at the trade show. Push a big gear slowly, like 30 rpm, on a trainer, and shift at some random time to the small ring. Don't let up on the pedals. The chain drops at the lopped off teeth every time.
Of course no guarantee if you have non-round rings or a dying battery.
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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson