The verdict
If you are a B2B team on Salesforce with enough lead volume to justify a dedicated platform, pick Pardot. If you sell to shoppers on Shopify and want SMS to bring in repeat revenue, pick Postscript.
Neither is a good choice outside its home. Pardot is sold on annual contracts, priced per organisation and only really pays off with the CRM link. Postscript is built around Shopify and billed per message, so a store on another platform should check the fit first. A small B2B team that is not on Salesforce would be better off with HubSpot, which is easier to start with and to change later.