Hi, I have the 42mm AT&T galaxy Watch. It works really well. The best battery life I can get is just under 48 hours.
The bigger version has a bigger battery so if it looks good on your wrist (& you have the money) it's probably a better watch to get. I pay $20. Extra per month and it's worth it to me. People say our phone calls are clear. It looks great too.
If you get one, (I have a black one) get a screen protector, and a Bezel & watch body protector. These watches get scratched so easily! Amazon has it all.