lvling up?

[Ishar]

If you have a level 60 sitting around, boosting is far faster, generally. And ROS bounties can be quite useful for that; though they've nerfed several of the really good ones I believe.

Regarding straight leveling? It's all about the same, really; doing the highest difficultly level that lets you complete quests at a rapid clip. Whether in ROS or not, this is sort of six of one and a half dozen of another. Probably nothing will ever beat act 2 "A Royal Audience" since it doesn't contain elites, so you can crank the difficulty way up. When I came back I didn't have a level 60; so just bought ROS and alternated A royal audience with playing through the entire campaign normally (when I got sick of repeating A Royal Audience). I believe I hit 70 somewhere in the ROS act.

You have to complete the entire campaign before adventure mode unlocks, IIRC.