From 58 you have a couple options:
Ramparts - Good for 1 run and turn in the quest you get from the boss
Blood Furnace - Good mob density but difficult to get out if final boss glitches, forcing you to walk all the way back
Shadow Labs - (imo the best) Clear all mobs up to the Inciter boss, then run out and repeat. Good for farming gold too and can be used all the way to lvl 78 if you don't want to quest a lot (will take a long time)
I do not bother with arena quests since there are so many people trying to do them all the time, it's not worth the hassle fighting other people for it
I've boosted a couple of characters through Scholomance now. Very effective to get them from early 50s up to 60/early 60s.
The run is a bit of a pain, so I have stationed two characters at the summoning stone in case I want to boost other characters.