Should I Defy Hircine?

Don't kill Sinding. Instead, help him kill the hunters. ... Now exit and Hircine will appear again in his stag glory to ask you if you killed Sinding. It doesn't matter if you pick "I failed" or "I disobeyed your orders" he will still commemorate you about turning the hunt around (hunters become the hunted).

Should I spare Sindings life?

If spared, it seems Sinding is ultimately unable to control his beast blood. If the option to spare Sinding is taken, even if the Dragonborn turned around and killed him as well to complete the quest both ways, he can appear later in a random encounter as a hostile werewolf fighting a guard from the local hold.

Should I take the ring to Hircine?

360 PS3 Sinding will sometimes reappear in his jail cell if the Dragonborn chooses to take the Ring. They can then kill and skin him, allowing them to have both the ring and the Savior's Hide. Wearing the Ring of Hircine and the Savior's Hide can crash the game on Legendary difficulty.