Miko's headline offer is 15% off your order plus free shipping, which applies to all shoppers regardless of basket size. This is the deal to grab if you want the maximum value from every purchase, since the combination of a percentage discount and free delivery makes it hard to beat.
All three active public deals give you the same 15% discount on your order. The key difference is whether free shipping is included. If you're spending any amount and want the best savings, go for the 15% off plus free shipping offer—this stacks the percentage discount with delivery savings, so a $50 order saves you around $7.50 in discount plus whatever your standard shipping would have cost. For smaller baskets under $50, this combination of discount and free delivery remains your best option since it protects you against high shipping fees on a modest spend. If you've already factored in shipping costs or you're in an area with cheap delivery, either of the straight 15% off deals will give you identical savings to the headline offer at checkout—just pick whichever one is easiest to apply.
If you're a new customer, signing up to Miko's newsletter is worth doing before you shop, since you'll unlock access to special offers and promotions that could beat the standard 15% deals on your first order or future purchases.
Remember that you can only use one offer at checkout, so when you reach the cart, compare what each option saves you on your specific basket and apply whichever one produces the larger discount. The 15% off with free shipping is the safest choice for most shoppers, but run the numbers on your total if you know your local shipping cost.