As you've found out, for EK and Kalimdor, you shouldn't allow Archeology above 375 until you're level 84 with enough AH greenie gear to get you 6500 gearscore or so. (Depending on server, this should cost 600-1000 gold).
Your predicament pretty much forces you to Outland or Northrend, unless you want to die a *lot*.

Twilight Highlands and Uldum digsites will most definitely cause you to get into an AB 'death loop', if you get an unfortunate site. As to which one is better, that depends on what artifacts you might be interested in. You will need to do both, if you seek the Professor title.
cheers,
chinajade