Don't know 'bout you, but I think the iPhone OS look is getting a bit tired. It looks particularly odd on the iPad (don't get me wrong, I like my iPad). It would be nice to see Apple move away from the dorky button look and adopt a more fluid interface a la Microsoft. So... to cut a long story short (too late), I vote for WP7 Metro UI.

iPhone OS 4 | iOS 4 multi-booted with Android 2.2 | Froyo

It's sad that Microsoft decided to go with icons-based UI on the Windows Embedded 7 aka Windows in the middle

The metro UI is MUCH more useful.  You can see, right on the tile, the most important information.  This make the whole "glance and go" metaphore actually work.  It's really odd to say it, but Microsoft is really innovating in the UI and interaction design space while Apple is just riding market share. Live Tiles all the way, baby!