as a long-time paying user of Instapaper who recently switched to Pocket, here are my reasons:

  - a desktop mac app is available
  - I really like the 2 View options (article view and text view) as I read a lot of technical articles that include code snippets and these are rendered terribly on Instapaper
  - the iOS apps are snappier and crash way less often
  - search is baked in the apps

the fact it was free didn't enter into consideration at all