I have been using the LG watch Urbane 2 LTE for a bit over 2 months now, and it seems to be the best offering for runners. Not sure about other sports, and what apps are available in that respect, but the battery lasts forever and ever, I can track my runs with GPS, stream music over BT, answer and initiate calls and txts, browse the web, etc. all while leaving my phone at home! Was lalso ooking at the MS Band 2, but the MS sales rep at the store said that it hardly manages a 2 hour run with GPS on before the battery dies, which is not enough for me.
I used the Samsung Gear S for a year prior to getting the LG, and it was great at the time, but battery would not even last a 2 hour run, and there were hardly any apps for it. The LG only uses up about 17% per hour with GPS tracking, BT streaming and cellular on. It may be because of improved battery management on AW Marshmallow, meaning that other AW watches hitting the market with the newest software will be equally awesome, or it could be that LG just managed to figure out how to preserve energy.
Whatever the case, I would wait out MWC to see if the LG is coming back on the market (roll-out was cancelled in November) and to see what other watches will be announced. I expect the Sony SW4 to be a great contender, especially if they add LTE functionality and keep it waterproof! The Moto 360 sport got bad reviews in terms of battery life when GPS is on.