I know its popular to do the crypt atm, and it is surely packed with mobs. Still i think its more efficient to just doing fields. Its more boring but it seems you will kill more mobs per hour instead of including crypt when it spawn.
when i was leveling my barb, i actually skipped crypts because i couldn't optimize my fury in there (hitting dead ends and whatnots) but i guess it's still personal preference since when i do crypts, surely i will end my run there and not go level 2, port out and clear fields
although i have seen people clearing fields first then going to crypts if it spawns