Usually events for me since the zones are so barren I can't find people to do DEs with.
WVW is an easy fallback if you really struggle with finding events (unless your server rofflestomps the whole map), you can pop up there and capture a supply camp, if you dont think you can solo it quick enough ask in chat if anyone is hanging around and wants to join, if that supply camp has 2 caravans there then that is 3 events. Or you can roam around the maps taking down traveling caravans and those flag capture points. The lake ones are very easy to take too.
If you are solo capping or following a zerg it doesnt take more than a quick detour to get variety and gathering.
kill amount is the only one you never have to think about --- http://psnprofiles.com/goatjugsoup1278 GW2 Character Name: Ranger Goat of Yogi, Guild: Knights of Chicken
Definitely the kill variety. In the higher level zones you fight stuff like Icebrood and Risen and they all count as the same monster. You'll play for an hour only to find you've killed just 3 out of the 15 mob types you need. --- Rest in Peace City of Heroes: April 27, 2004 - November 30, 2012. We will miss you. Cause of death: "Realignment of Company Focus" by NCsoft.
Kill variety. Its not god-awful or anything, but its definately the last one I have to get in most cases, and usually the only one that requires me to go out of my a little for. --- ~ Master of Electricity ~ Electro: 0518-6613-7620 - Pokemon White