You didn't think we'd come all the way to London to see the Samsung Galaxy S III (S3) and not put it up against the Galaxy Nexus, did you? Physically, you can see some differences, of course. The SGSIII is a little more sleek, a little less angular. The glossy finish (especially the Pebble Blue color) is easier on the eyes, certainly less industrial feeling than the GNex, especially when you trade the textured battery cover in for a smooth surface.
The displays are fairly close in size, at 4.65 inches for the Galaxy Nexus, while the Galaxy S3 is a full 4.8 inches diagonally. But in terms of display quality, we're going for the GSIII, which a the very least seems to have fewer issues with whites than its older cousin.
Under the hood, we're also going to pin a winner on the Galaxy S III. The Nexus is fast, to be sure, but something appears to have been put into overdrive on the SGSIII, even with Touchwiz and livewallpapers a'blazin.
We'd have no problem trading in Touchwiz for stock Ice Cream Sandwich, but maybe not all of it. The GNex camera app is spartan at best. Samsung's custom motion tweaks are a fun addition (for example: When you're looking at a friend's contact info, you can simply raise the phone to your ear to place a call), and S Voice is a competent interactive companion. (OK, OK. A Siri "competitor.")
Build quality on the SGSIII certainly is as good as on the GNex, if not better. It's a solid-feeling phone, though it does tend to feel a little more like a hunk of plastic, whereas the GNex has hints of rubber.
Our one turn-off in comparing the two phones is that for while we're not necessarily against improving on the Ice Cream Sandwich user interface, Touchwiz doesn't necessarily do so. The app drawer is decent enough and mostly stick with the ICS paradigm. But the Touchwiz widgets don't look anymore sophisticated than they did a year ago. And considering how far Android itself has come since then, it's perhaps time for something new.