The question further details the importance of this matter. "I spend more time on my browser than any other piece of software on any given day. Primarily because I use it at both at university for research and for entertainment (i.e. reading articles here)," the question reads, "The trend these days seems to indicate the browser is becoming more and more of a target rather than the OS."
I'd say that there are two parts to this question. Not only is it important to take into account the browser itself, but also the platform it's running on. It's better to have both a browser and a platform with a proven security track record than to just have a browser with a proven track record in security.
Browser-wise, you are most likely best off with either Firefox or Chromium (not Google Chrome, but Chromium). I specifically mention these two because you also care a great deal about privacy. Since Chromium and Firefox are open source, you can be reasonably sure there's no weirdness going on inside the code that you have to worry about. While browsers like Opera and Safari also have a good security track record, their closed-source nature means you can't check the code for privacy-invading weirdness. I'm not saying Opera or Safari contain such weirdness - just that you can never be sure.
This extends to the platform aspect of the equation. There are several hardened Linux distributions out there, which are completely locked-down from a security standpoint. However, even desktop-oriented distributions like Ubuntu provide you with a safe, secure, and Free/free operating system. Similarly, while Mac OS X and Windows are/can be secure too, the closed-source nature of these platforms means you cannot check for any privacy-invading stuff in there (no matter how unlikely it may be).
What do our readers have to say about this one?