The neck def isn't the best option you could get. It's not the worst, but not the best.
As for the jar? If you have 3500 spirit without the jar..
A) That's way too much even for holy
B) The jar does more then nothing with that much spirit, get an intel trinket.
C) 3500 Spirit = Means you like to spam way too many mana costly spells and spam spam spam, don't do that.