I use power-archiver, but mostly because it has both a windows and command
line programs. Some operations, like creating a partial directory trees in a
zip or rar file, seem to be easier when done via command line.
I like Winzip. I've tried PKzip, WinRar and several others. Unless you
are really cramped for space I would reccomend Winzip. It may not
compress quiet as much as, say WinRar bit I think it's the easiest to
use. HTH