To capture open-ended feedback via SMS and write it to a data extension, using a text-response message template with embedded AMPscript is the most suitable approach. This method allows for the dynamic handling and processing of the incoming SMS responses. The AMPscript can be programmed to parse the response and write the collected data to a specified data extension, making it an effective way to capture and store open-ended feedback. Reference: Salesforce MobileConnect documentation, AMPscript in MobileConnect