I think the fastest and easiest way by questing is to lv two classes to lv 20 with mobs/quest in howling mountain/silberfall.
After that you can go to Varanas to Hall of the Eye of Wisdom (sry only knew german name, so I hope its also so called in English).
There you can get your third class and port to Heffner gets unlocked. Just press K-Button and port there.
Do all quests there with your three classes (if you just want play two, also good).
I changed all 10 lv the class, so I got all up with usable quests.
As a well known player, it took me about eight or nine hours to get my three classes around 55/55/55 (maybe bit higher)
Perfect lv to start in Thunder Roof Hills. To get there you have to go to Aoutulia Volcano and speak to Mysterious Torroq.
And there it starts, the Epic Lvling journey to 100/100/100 just start the Toni and Morrok Wallinder quest row. (Countless guides on the internet)
If continue the quest line after reaching max lv you can also get all skills max with one or two classes, can't say exactly because I did some tq's and goblin game during this time.
I hope I could help you a little bit.
I took me one week to max my three classes by the way.
Best Regards,
Kaiza