I'm a big fan of Instapaper, but in the last few versions of iOS and OS X Apple have been rolling out Reading List as part of iCloud. It's a similar concept, both Instapaper and Reading List allow you to save content from the web for reading later, online or offline. They employ slightly different approaches, and Instapaper is significantly more feature rich.
However, as I tend to minimise the software installed on my system, I thought it only fair to give Reading List a fair shot in place of Instapaper for a while, and see how it fares. From the outset it would seem to me that Instapaper has one clear advantage: it's API. Innumerable apps support the Instapaper service, and predominantly this means that content can be effortlessly forwarded to your Instapaper account from any app that supports it or by using a bookmarklet in your browser.
Reading List does not have this level of third-party support on iOS (OS X has an Apple Script verb). The only way to forward something to Reading List is from Mobile Safari. This means, opening content in Safari first (which is relatively trivial, and usually requires just tapping on the link) and then saving it to Reading List. On iOS though this means swapping apps every time you want to save something to read later. It's a first world problem, sure, but it is unnecessary.
I expect to go back to Instapaper full time at the end of this little trial, which I expect to last about a week (or until I feel that I've given it a fair run), but we'll see how it goes. For the duration, Instapaper has been removed from my iPhone and iPad, and disabled in the apps I use that support it.