The Garmin Forerunner 255 is the better option because in addition to new training apps and metrics it also includes a new chipset that offers multi-band Global Navigation Satellite Systems (GNSS) support with multi-frequency positioning. This means much more accurate positional data especially in more challenging environments. The battery life is also considerably better; 12 days in smartwatch mode versus 6 days on the 745 and 26 hours in GPS only mode versus 16 hours on the 745 - making it a much more suitable watch for triathletes. Finally the Garmin Forerunner 255 is a good bit cheaper than the Forerunner 745.