I used sketchbook pro for a long time, but now I use Manga Studio 5. It has all the tools for creating pages such as a panel tool, speech bubble tool, different shading textures and tools as well as premade panel set ups. It used to be a bit pricey, I'm not sure how much it runs now. But it is worth every penny. Not to mention it will convert it to most file formats for publishing and what not.