For some time, I ran Readability and Instapaper side by side to see which one is capturing websites more accurately. As far as my results go, there are some articles out that Instapaper captures much better than Readability does.
Admittedly, I have also experienced issues with Instapaper, e.g. Instapaper completely fails to “fetch or parse” this article while Readability does not have any issue with it.
I am more and more coming to the conclusion that (from the perspective of the humble user) it may be a good idea to use both services, each where it performs better than the other.
That is, where is it written that it has to be either Instapaper or Readability?