Scaleable screen size HELP please !!

Hello everyone,

iPhone 6 sports a 1334x750 resolution (at 326 ppi)
iPhone 6 Plus sports a 1920x1080 resolution  (at 401 ppi)

My question is for what screen resolution should I work on my games in order to make the game universal for all iOS iPhone devices? (My games will mostly be in portrait mode.)
Can i used 960*640 also for Iphone 6 and + ?
Tried 1920 *1080 cause i read somewhere stencyl would scale it down but when i launched ios simulator it was a mess.
Tried to search the forums and a lot of users are interested in this question also.

Noone who could help me and many others out ?

Stencyl recommends 480x320 display resolution, but if you want to avoid blurry graphics on the 6 plus you'll have to use a width no larger than 310 (to use 4x rather than 2x graphics).

Scene size is a different matter, and unless using stretch to fit you'll want it to be larger than your display resolution.

Thank you for the help   rob1221