For bragging rights with my friend got a Samsung Note 2 so I go with iPhone 6 Plus so 5.5 is good for me. 

6 inch is perfect for a phone.
Just curious - why is this so important to you? I thought the iPhone 6 screen is pretty sharp already. Would you trade a full HD screen for a battery life decrease?
didn't vote...the perfect size is the size that works for you![]()
A 5.5" screen with slimmed-down bezels and a non-protruding camera. Also a minimum of 11 hours' heavy usage time from the battery. The 6+ has a good battery life but it needs to be a little better still, like it was with 8.0 through 8.1.1
The perfect "phone" size would be as small and minimalist and convenient as possible.
However, the perfect 'portable computer with many many built-in functions, including a phone' (also known as smartphone) size will vary depending upon how you wish to use that portable device, and how it overlaps with other portable devices you own.