It's not a matter of small or big hands; it's what you can do with the device and the comfort a bigger device brings to your eyes if you want to use it for more than making a simple call. A bigger device is also better for typing.
I have small hands; I don't have an iPhone 6 Plus but I have had one in my hands and just loved it in every sense. I thought it was perfect, including the size. The iPhone 6 is equaly a great device. However, if have to choose maybe I go for the iPhone 6 Plus.
What smaller iPhone? I don't see the point in something smaller than the iPhone 6, which is really good size if you don't like the size of the iPhone 6 Plus.