There's always the under-the-hood changes from Android upstream, and Samsung keeps adding customization options every update. Without rooting or 3rd party apps*, no other OEM comes close to OneUI's customizability. For me, that's a huge plus.
*I meant specifically 3rd party apps, because Samsung has the Good Lock suite of apps, which needs to be installed from the store. They work somewhat as a beta testing of features or advanced controls for existing features, and many of the features are added to new updates, for instance, the quick settings easy access up to One UI 5.1 (Android 13) is only available via Good Lock's Quick Star module, but seems to be built-in on One UI 6 (Android 14)