In my experience, the mechanical is never quite as accurate or reliable as the electronic. The stock advancer has parts that wear out and require maintenance, but an electronic pickup with solid components has none of those things. On the down side, if your electronic ignition has a component failure, it's often fatal for the entire system.
With a decent aftermarket electronic ignition, you're usually able to get some level of programmability, too. It's a lot easier to push a few buttons than it is to tweak an advancer.