The two options solve different problems
Pre-Soak extends contact time before the main wash, while Prewash is an active preliminary wash stage. Washer terminology varies, so the model manual controls the exact behavior.
Use soak time for compatible stubborn soil
A soak can help certain washable, colorfast items when the cleaning product directions support soaking.
Use Prewash when the machine and load justify it
Heavily soiled sturdy loads may benefit from a preliminary wash step, but extra mechanical action is not ideal for every fabric.
Pretreatment may still be better
A localized stain often needs targeted pretreatment rather than making the entire load undergo a more aggressive process.
Use product-specific instructions
Garment care labels, appliance manuals and laundry-product directions can be more specific than a general guide. Use them when they set a tighter limit.