Desktop app (I should qualify that is personal preference). Mine is less feature oriented and more I don't like being taken 100% out of the context of what I'm doing to switch to Skype or any Metro app (if it's running full screen e.g. you haven't snapped it to a part of the screen). In the desktop model I can have multiple things open in the same context without the jarring feeling of flipping back and forth (like if I'm reading data out of one window and inputing it into another).
In a tablet context, I find the Metro apps ok. In the desktop context I find myself avoiding them for desktop counterparts when at all possible (for the above reason). What I really think would be cool (and probably will never happen) is the ability to popout a Metro app into a window so I could use it in my preferred context.