In my opinion, I wouldn't buy this new Iphone right now because It's as new that people may not know if it works well. It may have some problems. Then, talking about its size I think that it's too big and the Iphone 6 Plus it's very bigger.
I have got Iphone 5S and in my opinion this size is the best one. I have had this mobile for one month now. I really like IOS system. Only Iphones mobile have got this system. The camera has a better quality than the other mobiles that I used to have.
One disadvantage of this system is that you have to pay for some apps applications but there are cheap. Another disadvantage is taht in Iphones mobiles you can't put a memory card. So each Iphone model has its own memory. You can chose how many GB you want in your mobile. However, the more GB, the more expensive.
Since they started making the first iphone in 2007, they have made 10 models until now. Last year, they created the Iphone 5C that is the improved version of the Iphone 5 but with worse material so that's why it's cheapper and people can afford it. As well, people like it because it's very colorful. Although, nowadays there are new models in the market people still buys Iphone 5C.