I agree with ComicRack. I was using ACV (Android Comic Viewer) before, but it would constantly lock up on me after a few issues, sometimes after a few pages. ComicRack hasn't given me any of those problems. The fact that you can alter the settings in regard to how to flip pages, go to next book, etc.
The only drawback is that the paid one is so expensive, and the free one has ads. The ads aren't that invasive though, and I imagine that the paid version is worth it (also lets you sync comics with your PC).