Assuming you really really really trust your partners, and that you completely see eye-to-eye on how future business matters will be handled and how cost struct

Assuming you really really really trust your partners, and that you completely see eye-to-eye on how future business matters will be handled and how cost structures will go as the business ramps up, use an LLC with everyone listed as a managing member. And meet regularly to make sure reality and expectations are aligned, and keep the books up to date. This will probably still go horribly for you if you are successful. Instead what you would be better off doing, if you are launching the product alone, would be for you to have controlling interest in the entity, be the only managing member, and treat your partners fairly but ultimately be in control. This might result in a happier situation for everyone (yes including your partners).