On a digital device, sans serif typefaces are easier to read.
I have a personal preference for Roboto, it's Googles attempt at Helvetica Neue.
I feel like I have to contribute since I am something of a font connoisseur (which is to say, I'm a font snob).
I have had some experience with Google fonts, and I think they do a good job with the selection and implementation of it. I agree that it should be kept simple and legible without fanciness.
Open Sans is a nice font which would work fine. It's a little fat for my tastes, though. If I had to pick a similar sans serif font, I'd look at Catamaran, Hind, Hind Vadodara, or Khula (the latter would be my choice).
Good to know there's a fellow designer around here. Although, I cringe every time I hear the word font, it's always been type or typefaces to me. Microsoft has made the word font, interchangeable now.