The Suginami Makai Koudou (or Suginami Demon Tunnels) Bronze run.
I'm soloing on a low level character because I feel this is more realistic to what people would actually be attempting to do when tackling this dungeon.
Tips:
Fire damage is a must here, and Electric will also be a lifesaver.
The Quickly Produced Hathor is probably the best demon you can use here, followed by the Wounded Cerberus and the Brave Garm.