IOS Resolution Scaling

Ok there are several answers, theories that attempt to explain how to scale GUItextures and GUItexts for Iphone 3, 4, 5, Ipad, Ipad Mini etc... But is there a definite solution for how to set up your game in one resolution perfectly and it will automatically scale for each and every other resolutions past and future, retina/non-retina, HD etc.

Obviously OnGUI is a big no no for IOS so I assume using a Matrix is out of the question..

But if anyone could enlighten me with a definite fix for this common issue which I would imagine most unity developers run into. I would like to fix this before I even start with the game as I have seen so many issues arise with its implementation.

So in short, one resolution for all?