I've done LDoA on a number of characters and Ranger was definitely the easiest.
You got +30 armor vs. elemental dmg, good against all Vanguard spawned Bandit Firestarters. Use Fire Imp to take aggro, stand back and pick mobs of. Especially with with Ignite Armor vs mobs. If /w secondary and while not taking damage, Frenzy is a good skill on your bar as well. Just don't bring Power Shot on higher levels, it's armor ignoring damage becomes inferior at higher levels.
Necromancer is quite good as well once you reach higher levels. Imostly used Blood Magic at low levels, while Death Magic obliterate your foes at higher levels. Deathly Swarm at high level will decimate your foes.
Smiting Monk should be quite good as well, especially against undead vanguard foes. Breeze to counter the heavy degen while smite dealing double damage. Shielding Hands can make you virtually immune in some locations.
Didn't play Mesmer but can imagine the buffed Empathy skill will be worth gold as both damage and protection skill. However only single target.
Buffed Fire Storm if ele.