Standard checkout is the easiest to use and initiates a direct transfer from your web browser wallet to the grant. However, the gas cost (transaction fees) for standard checkout may be higher.
For larger cart sizes (up to 50 for zkSync), this rollup checkout method provides a much lower gas cost, but requires several extra steps in order to add funds to a zkSync account.
For cart sizes 50+, Polygon checkout would be your best option, since Polygon doesn't limit cart sizes. Similar to zkSync, it requires several extra steps to bridge funds to Polygon, but again, offers much lower gas costs as compared to standard checkout.
Please visit the official Polygon documentation for more on the process.