I am on my second Iconic and always seem to hit the XP wall pretty quickly (levels 16 and 17). Currently I take level 15 and easily run GH (normally enough to level out with Saga Stone). Level 16 normally Necro 4 with Lord of Dust Chain. Level 17 things really slow down, hit some challenges, Harbinger Chain and Wheloon. Level 18 is Vale (nice XP quick quests) and some Inspired Quarter Quests, then hold till 20.
What are other people doing?