Note-taking: iPad (uncontested)
The iPad's Notes app is simple but deceptively useful. I routinely use it to type in interview and meeting notes, knowing the contents sync to my IMAP or iCloud accounts so that the notes are available to all my devices. (If only it supported Exchange's notes!) You can use multiple accounts, such as to keep personal notes separate from work ones, yet you also get a unified view if desired of all notes. What Notes can't do is format text, but it retains basic formatting such as boldface on PC-created notes.
Metro has no note-taking app. You could use OneNote in Microsoft Office -- optional in Windows 8, included in RT -- but its complex interface is hard to use on a touchscreen.