I was wondering which browser is the most secure today, Firefox, Internet Explorer, Chrome, or Safari on a Windows machine with the user running as a Power User/Administrator account.

This is not a question about which browser is the best because its the most usable, but more of a question if asked for security, which browser is the most secure given an everyday user's experience (JavaScript, Flash, Ads, etc).

Also, would the choice for most secure change if the user was running as a restricted user?

To clarify, I'm looking for an answer that's based in research on potential and common exploits and how long it takes for critical problems to be patched.