Ascended Gear
For WvW it depends on your build, but most would just link you to this: http://metabattle.com/wiki/Build:Guardian_-_AH_Frontliner
For bosses, stats can vary, but most of the time you’ll be fine with berserker gear. Some bosses can’t be critically hit, so you can pretty much just pick any gear that provides power but not precision or ferocity.