I'm a little late on this, but with the semi-recent announcement that Marco Arment has sold a controlling share in Instapaper to Betawork, I've been doing some thinking lately about why I've stuck with the app over the last year.
I became an Instapaper user not long after I bought my first iOS device (an iPhone 3GS in 2009). I was living and working in DC at the time, and Instapaper was a natural fit for my Metro commute. I've used the app for more than three years now, and I'll admit that it's fallen a bit behind the curve in featuers and update frequency.
At the same time, Pocket has become a popular alternative. With its larger, VC-backed staff, Pocket has been able to iterate on its product and add new features with regularity. Marco stated in his blog post announcing the sale that he chose Betaworks because it has the resources and the drive to take Instapaper forward in the way he envisions. I'm really excited to see where the app goes, and given Betaworks's track record, I'm confident that it's in good hands.
Still, I've tried Pocket a number of times, especially as Instapaper has become less current. Still, I always go back to Instapaper within a couple of days. The reason is that additional features and new designs are less important to me than the ability of the app to do its most important function exceptionally well.
Instapaper and Pocket are both at their core read-it-later apps. By this measure, Instapaper is still far and away the better app, because it's reading mode is significantly stronger. The font choices are better, the pagination function is great, and the chrome is kept to a minimum. Pocket, for all of its features, still hasn't cracked this simple nut, and while the app is broader, it is also not as deep.
The value of doing one thing very well is so often overlooked. It's also what often separates a good product from a great one. I'm very excited about what the future holds for Instapaper, and I'm definitely going to stick around for its next generation. The app has earned that kind of loyalty.