Mainly, the Vario has electronic timers that accurately dispense coffee with a small margin of error, of course depending on bean type and freshness. I really like it. I'm going to buy a second grinder for all non-espresso purposes, and was going to get the Preciso, but my wife is pushing me to get a second Vario.

It's arguable I guess, if the Vario's control of grind fineness is actually easier than Preciso's, but it would seem it's probably quicker (though I've not used the Preciso).
Also, the Preciso has small concial metal burrs, while the vario ceramic planar burrs.
Read
here for Mark Prince's review of the Preciso, and
here for a comparison of all the Baratza grinders.
EDIT: LOL, Shawn beat me to it!
Living the caffeinated life.