Here is my tips for a fast levelling before 50 and with a 80 in mentor :

0-5 : isle, TD, Darklight ... no need of mentoring.
5-13 : mentoring and start from the bell in Antonica to the BlackBurrow entry. Kill everything you find. You can grab your 13 in less than the time you need to travel to BB entry.
14 - 22 : BB or Stormhold with a 80 it's a piece of cake !
22-28 : Thundering Steppes, I used to kill gnolls near the entrance to Antonica but every groups of 2 or 3 is good.
28-30 : Varsoon or giants in Antonica.
30-40 : Enchanted Lands-Runnyeye-Rivervale.
40-50 : Lavastorm-Everfrost-Permafrost

Only bashing, no quests at all.
That's what I'm doing, don't know if it's the best way, feel free to comment or add some usefull informations
As I want to level as fast as possible I'm looking for the best path to get the 80 in no-time.