Unless you’re supporting really old versions of Android, you probably don’t need to worry about method count anymore, as Multidex is enabled by default since SDK 21. Total APK size is still something to keep an eye on, but there may be more important metrics, like runtime performance, and features. And kotlinx.serialization has pretty good runtime performance: faster than GSON, and slightly slower than Moshi. Feature-wise, kotlinx.serialization is newer and lighter-weight, but still does all I have needed from it. Personally, I prefer kotlinx.serialization mainly because of its multiplatform capabilities