Currently, the zoom icon for the toolbar is a dropdown list. Nautilus uses
a custom control with zoom in zoom out buttons and a display of the current
zoom level.

I believe that the Nautilus approach is better because:
- It predates Epiphany. Nautilus has been using this approach for some time.
- It's easier to zoom. Zooming is generally a relative thing; people don't
care whether they have exctly 75% or if they have 70%; they mostly want
"smaller" or "bigger".
- Using the dropdown list means clicking once to bring it up and moving up
and down to choose a new zoom level. The button method only requires a
single  click.
- It's consistant. It's easier to change Epiphany than Nautilus.