The new Adobe reader seems to be very fast, but taking high memory usage is still a issue.
Foxit have always been a good PDF reader and it's fast but PDF-xchange viewer is also worth mentioning here.
sometimes with large pdf files(such as pdf containing scanned images), foxit is comparatively slow in some activities (like re-saving that pdf after editing and organizing) than the pdf-xchange.
sumatra is good, simple fast and no-frills but it lacks highlighting option, something very essential, at least for me.