I did:

61-63 ramparts/furance
63-65 slavepens
65-67 mana tombs
67-69 sethekk
69-70 shadowlabs/magisters

You could do UB too, but at 63-65 I found the 2nd boss pretty rough. And well, once you get a taste of mana tombs at 65+ you won't wanna leave anytime soon