Do you think you could comfortably fit them in your pocket, and use them while on the bus or train without much trouble? i'm having trouble decking which one to get, and the deciding factor is portability, because i commute a lot too and from university.
The big phone can fit in all my work pants pockets (I wear suits generally M-Thursday). I have some slim jeans that the phone may stick out length wise.
Sometimes on the train, I hold on to a pole and play games one-handed with my current 5c. That will be impossible with the 6+. There will be more two handed use.