Im a huge fan of the Uniball Stabilo White Gel Ink Pen – I think it ROCKS! A close second is the Ranger Inksenssials as it does write on different surfaces unlike the other brands but its not WHITE enough for me.
You can see below the doodles I did to show you the difference in the whiteness between the Uniball and the Ranger pens:
See how much brighter that Signo pen is!!! It writes a lot smoother too and isnt scratchy like the Ranger pen – I hate scratchy pens!