I tried uld at lvl 40 with a mage power lvling me. I didn't get that much xp there. Then we did a zf run, the xp there was better.

I would do sm cath till 40
then zf from 40-45
then scholo 45-55 (currently doing now getting about 2.4 bars just clearing the first room in 15 min then reset)

But if you have a lvl 70 pally there is a trick in ST that you can do from 35 till 50.