Should I buy the iPhone 6S or 6S Plus?

Getting a new phone tomorrow, wondered if any one had experiences with these phones? I ideally was going to get the Plus model as I need a long battery life and a good camera however I'm now wondering if it will be too big to live with, and also taking it to school with me.

I prefer the 6s. If you want to actually reach your thumb fully across the screen and not have it falling out of your pocket.