In following the outline, I will rank the features in terms of importance to me as an individual. These rankings are for suggestion only and by no means do I claim to represent any demographic.
Essential: Page Load Time, CSS, Javascript, Page Load Reliability, Memory Efficiency, Standards Conformance
Important: Flash, DOM, Startup Time, HTML5 Hardware Acceleration, HTML5
Nonessential: Java
Unimportant: WebGL, Silverlight
Now, the reasoning.
I usually launch a browser once and keep it open until next reboot. However, there are times when I must close and re-launch the browser. This happens because of memory inefficiency and so this explains why I place Memory Efficiency in the essential category. In this respect, Firefox and its derivatives are notorious offenders.
Page Load Time is there because some browsers like IE9 takes slightly longer than others to load certain sites, especially if the site is very complex and rich in content.
Page Load Reliability is there because some browsers such as IE9 and Safari fails to load a page and instead spends an eternity just spinning in circles.
Standards Conformance is there because we are moving towards converging on one web standard that works for everybody. We don't want a repeat of the IE/Netscape/Firefox/whatever era.
I've truncated some of the explanations as I don't feel warranted to explain everything, but this should give the editors a snapshot of where this particular enthusiast and power user places his attention.