- Too many ways for me personally because bugs occur. It can happen that you entire char become corrupted. It is not often, but it happens, that you read about these stories here that quests become impossible to complete for a person, and it is often due to some weird MP bug.
- Game is not balanced around multiplayer, it becomes too easy and you will not learn it properly IMO.
- Friendly aura bugs. Ever heard of players killing each-other with e.g. Aura of censure?
^ this. But, at some point you need to get into main campaign and start getting reputation.
Personally, I first go to crucible and equip difficulty skip tokes and Lokarr set. Then I go to Main Campaign in ultimate and gather some lore notes. I then go to the first quest to kill zygotor or what he is called. When he has spawned, I drink exp pot and read all lore notes - this brings me to level 15 or so depending on how many notes I gathered. Then I pump some points in stats and skills and kill that zygotor dude and then hand in the quest(s) in DC. When this is done, I go to main campaign in Normal and start to farm shrines. This leveling method is much faster than crucible IMO.
Devotion shrine hopping method - just use the difficulty skip token.
The reward of getting one char to ultimate and being revered with Malmouth faction will save you guys LOADS of leveling issues in the future. At some point, I strongly advice you to do this