I have the following accounts:

Account 1 - original Veteran account of mine
Account 2 - referred Account
Account 3 - UNLINKED and contains my level 70 feral druid transferred off Account 1

1-10: Quests, easy peasy
1-15: Deadmines
15-20: Stockades (much better xp rate due to more elites)
20-40: SM Cath (you will come to loathe this place)
40-50: ZF
50-58: Scholomance

Some tips especially with a 70 feral druid:

ZF - For the most part it's quicker for me to DPS down in kitty form each mob one by one. Remember the instance can be reset so if you're running more than you're killing then you're wasting XP per hour. It depends how bored I am but as a general rule I clear in a straight line through the instance and backtrack down the tunnel to the left when the option comes. That's constant killing. I get back to the entrance in seconds and reset. At Level 45 I'm dinging every half hour, no doubt some do it quicker in AoE but I can live with that timescale.

Scholo - At 50, they're levelling up about once every 45 minutes. I can clear The Reliquary in 15 mins bang on, get out and reset. I loot as well simply because I still get a good price from the Lifestealing recipe on Bronzebeard and the cloth sells well. Good cash as well, it all adds up. What I particularly like about that room is that you can park your toons at the top of the stairs central on the balcony and once you've cleared the one armored skeleton thing that patrols that way, you can forget them, kill and just pick them up again on the way out.

First group (first ever multi-boxed) has taken a while but the second group I've boosted are at Level 47 with 18 hours /played. Note I leave my toons logged in for smokes/coffees/phone shit all the time.

Like I say, some may do it quicker but for this boosting setup, it's the fastest I've managed to nail it.