According to Google, "ga.js is a legacy library... we recommend you use the latest version of this library, analytics.js".
In particular, "Universal Analytics introduces three new versions of the tracking code" that can more accurately track various devices: "gtag.js JavaScript library for websites, the Analytics SDKs (v2.x or higher) for mobile app tracking, and the Measurement Protocol for other digital devices, like game consoles and information kiosks."
Source
According to Google, "ga.js is a legacy library... we recommend you use the latest version of this library, analytics.js".
In particular, "Universal Analytics introduces three new versions of the tracking code" that can more accurately track various devices: "gtag.js JavaScript library for websites, the Analytics SDKs (v2.x or higher) for mobile app tracking, and the Measurement Protocol for other digital devices, like game consoles and information kiosks."
Source