Oriental Trading's headline offer is free economy shipping on orders of $75 or more, which applies to everything you buy. But the real savings come from the tiered discount deals that stack on top of that shipping benefit—and which one works best for you depends entirely on your basket size.
Spending around $75 to $149: You'll qualify for free shipping, which is a solid start. If you're in this range, the $10 off deal when you spend $75 gives you immediate savings alongside your free shipping. Once you hit $150, you unlock better value, so if you're close to that threshold it may be worth adding a few more items to your cart.
Spending $150 to $299: You have two main options here. The $25 off when you spend $150 deal delivers stronger savings than the $15 off alternative, so go for the $25 off offer in this bracket. The $20 off when you spend $150 or more is also available, but the $25 off beats it, so compare both at checkout and take the larger saving.
Spending $300 or more: The $40 off when you spend $300 or more is your winner at this spend level. That's the biggest absolute discount available and will save you more than any of the lower tier offers, even when you factor in the percentage discounts from the various sale sections.
If you're shopping sale items specifically, Oriental Trading runs several category and seasonal sales (Back to School up to 65% off, Summer Deals up to 50% off, Fall Decorations up to 50% off, and others) alongside their general "up to 68% off sales items" promotion. These percentage deals can save you more than the tiered discounts on eligible products, so check whether the items in your cart qualify and compare the final price against what the spending thresholds would give you.
Remember that you can only use one offer at checkout, so add your items to your cart, note the total, and pick whichever deal produces the bigger saving. The free shipping kicks in regardless once you hit $75, so your real choice is between the tiered discounts and any applicable sale pricing.