I wouldn't take your experience of the Z1 as an indication of Android in general Vita, as even for me it feels a little backwards at times.
Hold out for KitKat on the Nexus 5 and give that a go before writing it off completely as it's much more a fair comparison being as it will be Android as intended rather than Sony's take on things.
In my opinion, the Z1 is a slightly odd shape which doesn't bode well for comfortable browsing if you have little girl hands like mine, and is slightly too large simply based on the bezel thickness. Not only that, but having on screen buttons realistically leaves around about the same usable screen size as my One X, but with the unfortunate downside of having an inferior screen. Rooting the device would allow you to make the on screen buttons disappear, but then you can't use the bloody camera if you do. Nice one Sony.