I don't meant to be a Troll, but "Most Efficient Way" is very subjective, so as "most fun way". It all depends on what you enjoy doing.
There are several ways to achieve Exotic Level Gear.
- Dungeons Explorable Mode: Farming on Dungeons os probably the fastest way since you are rewarded with gold after completing each Path and rewarded by "Badges" of each dungeon, which is usable to buy Exotic Gear in Lion's Arch
The gold itself from the dungeon loot + rewards can also be used to buy Exotic Gear on Trading Post. Also, you are rewarded with small jugs of karma (400 karma per jug) everytime you kill a "boss" or make "any progress" in the Dungeon Paths. Usually around 3x little jugs per Path which grants you 1200 Karma per path run.
So with dungeons you get KARMA + GOLD + BADGES (which are all usable to buy exotic gear)
2.Karma : I would say that the best way to farm Karma is by having an active World vs World guild. By capping Towers, Camps, Dolyaks, Sentries and Keeps you may be able to keep the Karma Going. Also, never forget to do the daily Achievements, which rewards you a jug that grants you 4.5k karma. Each Piece of Invader's gear (WvW Karma Gear) costs 42k Karma.
As my personal advice, i would keep all the jugs and consumable karma sources, and wait until your guild activates the +15% Karma boost, and use them. You may also buy a Karma Booster and use all the jugs during the booster, that will stack with the guild's bonus
3.Gold Farming : With the proper group / Gear you can farm up to 15-20 Gold per Hour in Citadel of Flame Path 1 Dungeon. With 20 gold you can buy any full set of exotic gear in trading post. Ofc those situations are rare, but in a "slow pace" you can farm around 1-2 gold per hour in Cursed Shore
4.Leveling Crafting : Crafting may be used to craft your own exotic sets, but this is by far the slowest way (i won't say it's not fun, it is up to you, personally i find very boring to keep on gathering stuff over and over again).
Fastest Way : Dungeon (Citadel of Flame Path 1 or Ascalon Catacombs) -> World vs World -> Gold Farming -> Crafting
"Funiest" Way (in my opinion): World vs World -> Dungeon -> Gold Farming -> Crafting
I hope it helps