Depends on what you want. If you have a decent desktop PC, Windows 7. If you have a very old PC, or a very underpowered netbook, then Chrome OS.
Chrome OS is really just Linux with the minimum install needed to run web based apps. The goal with all the apps that would run in Google Chrome, would run in any web browser, so all the apps would run on Windows 7 (or anything else really).
If you have a need to turn on your computer and do web based stuff in 10 seconds or so, Chrome is a good option. If you need to do anything not web related, Windows 7 is the answer.
If your not in the ultra portable world, they really don't compete.







