I like the thread. But lots of guessing and personal preferences.
How about we add some figures?
Just doing 15 min grinding sessions, noting down XP progression.
1) Iquan Cave, end
2) Way between Iquans and Mountains towards Remgard
3) Way towards Remgard, between plaguestriders and Remgard
4) Green Maze between the snakes and Hirathil
5) Cave system just before Lodar
For me, the 4 Green Maze was fastest so far.
In 2 and 4 I can go in guns blazing, smacking and whacking without taking much care or saving often.
In areas 1, 3 and 5 I need to be more carefull with my current char, save more often, load every now end then when I die, which slows down progress.
With more damage output and/or more block, things might change
With my recordings and experience so far, I'd suggest 2 and 4, if you struggle and need to take it slow in the other areas.
What's the speed in your area with your Character?