[Jakob]

I agree with hide() and show(). Their performance is not that important since they are a swiss army knife and hopefully not used on too many elements at a time. The bad performance of .css() in the jsperf above is strange, though.

Profiling shows that it is not one big function but many small which accumulate. The camelCase function alone takes 3% of the speed in Chrome, the internal access() structure takes nearly half the time itself.

Speed could be achieved with the byte cost of specialised functions for easy cases like css(key, value) where you can skip most of the checks and queuing.

This shortcut for show/hide is roughly 16x faster and should remain more or less so even after extending it to cache the previous style and adding common exceptions for <tr>, !important, etc. Shortcuts like those could be used if it is clear that the chosen function signature is very easy like $('p').css('display', 'none') so all other checks can be skipped but would add to the payload of jQuery.

    $.fn.cssDisplay=function(show) {
      var d=show?'block':typeof show==='undefined'?'':'none',
        length=this.length, i=0;
      for(;i<length;) {
        this[i++].style.display=d;
      }
      return this;
    }

I’ll have a look into a more generic and faster .css() solution.