Best use of gold shells for new player?

I have enough gold shells from underwater adventure to get one thing. I currently only have durian hammer as far as s epic weapons, but I'm not sure I like it enough to stick with it. Would I be better grabbing mecha titan just in case, or should I get salty fish for the shield boost, or should I just get another s weapon chest? I'm not far enough to equip mecha titan right now (I'm at warrior 2-2), but it seems super strong for durian in the future