If you don't know what you real need is, you'll lost.
I want to upgrade my phone to new model, while do not know which type I should buy. Usually I'll select the cheapest one, but this time I can not do the same thing anymore.
My phone is iPhone4S, and I feel the performance is slow after I upgraded the iOS to 8.1, and more uncomfortable is that it can only run in 3G mobile network. My phone is China Telecom phone, while means if I want to use a newer model to support China Telecom 4G, then I'll have to use iPhone6 or iPhone6 Plus.
I used a phone with 4.8 inch screen, and when I read PDF file, I would have to move the page left and right frequently, so at that time I hoped to get a phone with 5 inch screen. So for new iPhone6&6 Plus, one is a little smaller, and another one is a litter bigger. 
I compared both of them:
6 plus has bigger screen with more attractive PDF reading experience, and more strong battery usage time, and more weight. I believe I'll have to wear a bag to carry it.
6 is more portable and lighter, with better single-hand operation experience, but I'll have to move page again when I read PDF file.
Of course, the price is different, but it's not a critical element.
I hope I can have enough money, so buy both of them, then carry anyone of them, and leave another one home.
Or use one, and put another one under the desk leg. 
