I tried Instagram but it's a bit limiting, the current favourite is Tadaa. The filters and editting features are far more comprehensive while not offering the full range of Photoforge or Snapseed say. That said, most shots tend to enter a few different apps anyway so no big deal there. Tadaa seems to offer a real community too and I think is the most popular sharing site in a few parts of the world. I tried EyeEm but wasn't impressed.
The snobbery of the "real" photographers using "real" cameras is astounding. The best camera is the one that you have with you, ever heard that phrase before? I've been shooting a photo a day for 6 weeks, many times when the other 3 "real" cameras are at home. The iPhone forces me to look at subjects differently so I welcome this refreshing direction that dept has taken (this post typed on my Canon 5D Mk 2).
Get a weekly update of all that's new in the digital
photography world by subscribing to the Digital Photography Review