What's the best Fitbit to get? What are their differences?

I have seen my friends withthem and seem awesome. I just joined weight watchers and have been slowly but surley loosing weight. I want to buy one, possibly on Amazon prime but there are so many choices. I have an Iphone 6 plus. Would like it to track my cal burned steps and stairs. Not so worried about heart rate because id on't really know why I need to know that.

The flex doesn't count stairs, just steps, calories and sleep, that's the one I have but the Charge HR and Surge do, the reason people prefer the ones with heart rate is because generally calories burned are far more accurate when measured using your heart rate included.

I like mine but I know I burn more than it says I do because if I eat what it tells me I have burned I steadily lose weight and I do sometimes wish I had gone for one with HR for closer accuracy, none are exact though, even a wearable device is still a guide even if it is a pretty decent guide.

I would read reviews and compare the models to see which one fits your needs best.