I bought the QNAP for my house, My office used the Synology (that i managed) until we went WFH and i 'adopted' Synology and brought it home.
The OS on the QNAP (QTS) is easier to use and IMHO just better than DSM (Synology).
Managing the drives, Time Machine, RSYNC, or integrating with cloud services like BackBlaze B2, Google, and Amazon is (IMHO) just better done on the QNAP.
QuMagie is QNAPS photo management software (object/people recognition and cataloging) is 100x better than Photo Station on Synology. So if you are going to be doing any backing up/organizing of photos keep that in mind.
QTS on the QNAP
DSM on the Synology
QuMagie (QNAP)
Photo Station (Synology)