After trying several apps in this category, I found Gifit a simple, reliable GIF making app allowing me to quickly and easily convert my videos into animated gifs. The interface is designed uncluttered and lets you get the job done in just a couple of taps.
Please also note that the camera roll doesnt render animated gifs and shows just a still image but when you share it through a compatible app, such as iMessage or Twitter, the animation cranks up.
However, Gifit crashes everytime I take a go at converting a rather long video (i.e. a 45 seconds video). I hope to see a fix as it takes too much time to convert and then it jumps to the home screen surprisingly.
One more annoying problem that should be fixed is that it zooms in the video, making the animated GIF useless in some cases!
incineration about Gifit - Super Simple GIF Maker