It should go to the draw pile, but I assume that's what you meant to write.
Develop indeed takes precedence: Den of Sin means that the card goes to hand instead of discard pile first. Develop then moves it to the top of the deck.
Marcus, WHY does Develop take precedence? Is there some sort of default Dominion rule that applies here? I'm thinking of Fortress, where--when it's trashed--seems to always go back into my hand, regardless of the wording/instructions on the other cards, which might call for the card to go into the discard pile, on top of my deck, etc..
I guess what I am really wondering is: Is there a list of special card combos, where at least one instruction on Card One directly conflicts with an instruction on Card Two? And, if so, is there an easy way of knowing which card's instructions takes priority? Or is it a question of memorizing each of these oddities?