The The Bad Peach page currently features the $25 off voucher above, which takes $25 off orders over $99. That voucher is best for you when you have a mixed cart or non sale items and your subtotal will clear the $99 threshold. If you are buying sale products that are eligible for the summer sale or the up to 65% off sale, those percentage discounts can save more on high value sale purchases.
Small carts under $99: you cannot use the $25 off voucher on orders under $99, so your best move is to shop sale items if possible. The sales apply site only to sale product pages; the summer sale gives up to 53% off sale products, and the other sale gives up to 65% off select sale products. If you have a $90 cart of full price items, no voucher applies and you would pay the full $90. If that $90 is all eligible sale items then a percent discount may apply at checkout.
Between $99 and a few hundred dollars (mixed or full price goods): use the $25 off voucher above when your cart is not made up of sale items, or when the sale prices do not beat a flat $25 saving. On a $120 order, for example, the $25 off voucher takes $25 off, leaving you with $95, a saving of $25. (Original $120, fixed $25 off, final $95, saving $25.)
Large sale only orders: if your cart is made up of sale items that qualify for the percentage discounts, the percentage deal will usually beat the $25 voucher. On $150 of sale items at 53% off, you pay $70.50 and save $79.50. (Original $150, percent 53% off, final $70.50, saving $79.50.) On $200 of sale items at 65% off, you pay $70 and save $130. (Original $200, percent 65% off, final $70, saving $130.) Note that the up to 65% off sale states the offer cannot be combined with other promotions, so you would not be able to use the $25 voucher on those same items.
First time newsletter signup: signing up for the newsletter may give you future special offers and promotions, but the page shows no immediate signup discount amount, so treat it as a way to get future deals rather than an instant saving for the current cart.
Choose the option that gives the lower total. If your cart is mostly sale items eligible for the 53% or up to 65% discounts, use the percentage sale that applies to those items because it will usually leave you with a lower final price than a $25 reduction. If your cart is full price or mixed and totals just over $99, the $25 off voucher above is the simpler saving. The 65% sale explicitly says it cannot be combined with other promotions, so do not expect to stack that sale with the $25 voucher.