I prefer Open Sans:
http://www.google.com/webfonts/specimen/Open+Sans
Ubuntu is another great neutral sans font with a little bit more style:
http://www.google.com/webfonts/specimen/Ubuntu
IMO Gil Sans is a little bit too 'irregular', especially on a high-DPI screen like the Glos, while Avenir doesn't render well at all on the Glo because the stroke width is so narrow. Setting it 'heavier' using advanced settings makes it look weird imo.