Pandaria

I like doing the Pandaria Masters and Spirits.

I've worked out a route that lets you defeat all 11 in under an hour and if your toon isn't max level, about 40% of a level. More with heirlooms and a garrison potion.

Pet Treat and Safari Hat active are a must also.

Leveling

I do a sort of S shaped route starting at Hyuna in Jade Forest.

The first two "Legs" gets me a pet to 25 from level 1 each.

After I finish the Flowing Spirit I either start with a level 14 or higher pet and take it to 25 or just top off a couple of 20+ pets with the last 3 fights.