When i first did it when it was relesed i stayed in kalimdor most of the time going to eastern kingdom once in awhile for more troll digsites. And correct me if im wrong i think they changed it so when are are done with all the rares for Night elf for example the amount of night elf digsites will be reduces infavor of those u have not completed the rares with yet.
And i think no mater how u do it, even if u just stay in kalimdor its still gona be slow, if your not a dwarf then it will go a lite faster since u get more fragments.
but i think staying kalimdor is faster quite many digsites there that are not to far from eachother.
I'd go to Outlands (until 525) and Pandaria (from 525 onwards) as soon as possible. They are both fairly compact continents. Pandaria has the added benefit of being able to purchase fragments of choice with completed Pandaria artifacts. It might be tempting to get back to Kalimdor when reaching 450 to get some Tol'Vir sites, but it's quicker to just stay in Outlands.
Kalimdor would be the best choice to get to 300, especially if you're Horde. Alliance cities are all tucked away in the northwest corner, but you still have Uldum and Mount Hyjal as possible starting points. Horde gets Thunderbluff and Orgrimmar as additional starting points.