It does not sound like you are planning to race with the watch, so any of three would do well in that regard. However, if 10 hours of battery is a priority, then the Fenix 3 is really the only option. The 735XT seems to crap out at around 10.5 hours in a triathlon. The 735XT is likely to be one of the most comfortable for 24/7 tracking due to its weight and size. The AW requires special apps and charging logistics for 24/7 HR and sleep, while you just have to remember to charge the Fenix or 735XT once a week or so.