Shader "Fastest Shader" { SubShader{ Pass{} } }

This question doesn't mean anything. The fastest shader is probably the one above, that renders black. (On other platforms, it might be a shader that renders absolutely nothing, but I'm not sure this is true on iPhone, due to oddities of the tile-based deferred rendering system.) You need to figure out what you need something to look like, and choose a shader based on that. You can always add bells and whistles if your framerate is high enough, but you need to nail down what is most important first. For instance, just a plain texture is frequently all I need. Here's the fastest general-purpose shader that does that.

http://www.unifycommunity.com/wiki/index.php?title=Texture_Only