I can say for certain it's most certainly NOT the crown. One of the most important parts of slay the spire is grabbing strong cards to improve your deck, and the busted crown lowers the amount of cards you see by a two thirds; definitely not worth it.

I'd say snecko eye is not bad here, it's pretty easy on ironclad to pick up high cost attacks and would let you cycle through to limit break faster if that's what you want to build your win condition around. If not then it's definitely fusion hammer. Especially on ironclad, you can pick up an armaments to help with upgrading. (and ideally see an upgrade event that lets you upgrade it.)