BitDefender and Kaspersky have been on the roll for some time now, it's a question of personal preferences about granularity of settings and performance, since they seem so evenly matched in their capabilities, as evident by various AV tests.
BitDefender 2013 is heaps better than its predecessor, 2012, which marked a significant departure from their products up to that point. They switched to almost all-encapsulating interface and severely limited the available options, for silent and easy-to-use security. I'll not mention the performance, functionality and usability issues of that release, since that's all in the past - 2013 versions are very light and responsive, with almost non-perceptible impact on performance. Startup can still be affected, however, as well as watching video content, but the overall improvement compared to last version is pretty impressive. They've also made improvements to their compatibility with other security products, at least that's my experience with it. Updates are a point to consider - frequent and rather large, a sign of scope for development effort to improve effectiveness and reduce redundancy.
Kaspersky on the other hand has kept the countless settings, which can be helpful in trying to mitigate the more noticeable system impact, as well as getting as paranoid or as lax as you feel like in terms of levels of protection. Hardened settings will cause noticeable drag, but you can safely take it down a notch or two and still be very secure. If only they can achieve the sort of turnaround in performance and optimization that made Norton one of the lightweights of the industry...
Application control to me is pretty impressive, too. They've dropped Safe Run in 2013 version and replaced it with Safe Money instead, unlike BitDefender which kept the sandboxing functionality [in their browser toolbar] and implemented SafePay too. The online protection is very comprehensive and effective.
ESET to me just doesn't have that distinguishing point of difference or advantage, the unique selling proposition to make me get interested in it, it just works - lightweight, simple and reliable, poised and accomplished enough to not cause any ripples of discontent, effortless performance which could be mistaken for mediocrity.