Opera is too quirky for most people...
...who are not a bit quirky themselves. I am quirky myself and tried opera several times over the years but simply could not live with it, although I can understand why some people do like it, especially with very fine grained control over individual site security etc.
Since firefox changed to the awful 4+ i have bizarrely started to use IE9. I have not used IE of my own free volition ever, I even preferred Netscape when there were only the 2 choices, but now IE9 is very safe if on limited rights account and MS are doing a much better job that Google and others at identifying and blocking malicious sites.
I recently carried out my own tests and the MS solution was surpisingly effective, and together with the blocking from Malwarebytes Pro it has stopped almost all of the really nasty things that I threw at it, and the rest was stopped by PrivateFirewall HIPS. MS Essentials is also there to check only downloads and incoming files onto the system as an extra condom, just in case.
Back to the point, MS are doing a much better job these days,apart from the very rare false-positive mentioned here, and in some cases are better than the competition, strange as it seems to me, but my own tests have proven it. Professional tests have shown that MS actually have one of the most impressive fals-positive rseults of any AV, but Google definitely behaves like a trojan and so they deserve it.