It's great watching a newly tamed pet jump from level 1 or 30 or 45 to 65 all in a flash. But then you've still got five levels to go. Of all the places I've tried leveling a newly tamed pet so far, I am happiest with the Death's Door region of southeastern Blade's Edge Mountains.
It's a very compact place, it's easy to get to even with a very slow flying mount for both Horde (from Mok'nathal Village) and Alliance (from Toshley Station), and it's loaded up with mobs of level 68-69 - enough to generate good quick experience, not high or tough enough to be a pain to deal with - and with plenty of places to pause to rest, recuperate, go afk to read blogs for a few, or whatever. It's also a nice source of some Cenarion Expedition reputation along the way, thanks to a quest chain that starts with a damaged gas mask dropped by any of those fel corruptors who roam the area north of Toshley Station.
By the numbers, there's a good chance your level 70 hunter is Aldor. Something like two-thirds of level 70s who have an Aldor or Scryer reputation went with the Aldor. If so, then this is a good place for you: it's loaded with Marks of Sargaras. I've been raking them in at 30 or so per hour, on average, and sometimes better than that. But even if your hunter is Scryer or unaligned, the marks are worth gathering. They're in much shorter supply than Sunfury Signets, which means they auction at better prices. It's money on the hoof.
A couple of hours this morning, including idle time for blog reading, IM chatting, and like that, got me the 80 marks I needed to get Tivara to revered with the Aldor, and it got Timmorn (seen above gnawing on a Death's Might demon) from 66 to 68. Good stuff!