Clients usually do not know what "Original", "Standard", or "Web" means. They only know where they want to use the photo. Your job is to make the choice feel simple.
Original is for full-resolution delivery
Original files are the full files you uploaded. They are best for full-stack delivery, archiving, large prints, or clients who specifically paid for full-resolution files.
Standard is the everyday option
Standard downloads use the 1200px generated file. They are easier to handle and still useful for everyday sharing when the client does not need the full source file.
Web is for fast sharing
Web downloads use the 400px preview file. They are intentionally light: quick previews, messaging, and places where file size matters more than detail.
Tell clients what to pick
The best setup is not just offering sizes. It is explaining them in plain language before the client clicks download.