As a consumer, how should I determine whether to get a 4.7 iPhone 6 or 5.5 iPhone 6 Plus? - 1

As a consumer, how should I determine whether to get a 4.7 iPhone 6 or 5.5 iPhone 6 Plus? - 2

That would be up to you. Whatever size you think works best.

Read reviews or play with them in store to see what you like most

I will make it simple for you, if you have big hands get the 6s, if you do have big hands get the 6s Plus, unless you have average sized hands, love watching media, and want the extra features the plus comes with over the 6s (Bigger Battery, Bigger Screen, OIS, etc) hope I was helpful

Depends on who you are.
I already know I will not be getting a 5.5 inch model. I don't want a phone that big, and I will avoid getting one for as long as I possibly can.
On the other hand, I know people who would never consider the 4.7 inch model - which is why Apple is introducing the 5.5 inch in the first place.
And then there are people who don't know yet. They love their iPhone, would never get an Android or Windows phone, so they never seriously considered anything larger. Those folks need to go to the store and see for themselves. Put it wherever they like to carry their phone, hold it the way they normally hold a phone, see how it compares in terms of comfort with the 4.7 inch and also their current phone. I doubt anyone would actually prefer less screen real estate, so it's all going to be about how the phone fits them, physically.

Use them at an Apple Store or otherwise & see which you would prefer to handle on a daily basis.