I think the basin in Magician quarter would be the best. Duskbringers have the highest chance to drop shards. Also, many lower levels just light this basin and leave which leaves lots of the creatures to kill.
As a side note if you just want shards you would probably be better off levelling up a new character, picking Kazordoon as a city, and lighting the basin there. You wouldn't get the shards until after the event is over but would be able to sell them before the event starts next year. Also, you would get another 20k+ worth of items.