The Garmin Fenix 6 series is the top of the line range of activity and fitness trackers available on Garmin. The Fenix 6 series includes the 6, 6S (smaller version), 6 Pro (a version with music, WiFi, and maps), and the 6X (which includes all the features of the Pro with better battery life). That being said, basic functionality between them includes the best GPS tracking available on the market for several activities with detailed information based on the data.