It’ll likely come down to which one gives the biggest discount. The new shopping cart only allows using one discount code at a time, the bulk order uses an automatic discount code so you are not able to use two anymore.

Shopify doesn’t natively support bulk discounts so an automatic discount code is the only method for doing such a thing. Most of the experience in Shopify is MUCH better, that’s the one thing I’ve found so far that isn’t.