Hi Prodijy,
Choose whatever item you feel would help you most. If you have to choose between getting the Nobleman's sword or holy dagger choose the sword. If you feel you have a very powerful sword, you probably won't need a holy sword. You might instead consider getting a holy amulet when you decide to make the sacrifice. Save before making a choice and reload if you're not happy with it.
Hint: The area you're looking for is near the church hidden by some trees.
Spoiler: Click
here. Thanks.