Personally I use Paint Tool SAI (for everything, not just my comic). I haven't tried other programmes because i'm so comfy with sai. the cheap pricetag ($25) and user-friendly interface is great, plus you still have the ability to download infinite user-made brushes (there are some really great ones online!). only downside for me i've found is the lack of a polygonal marquee tool, especially since my speech bubbles are polygons... plus you can't do text in it.
so i do have to use photoshop for lettering and sometimes adjusting bubbles, but it's hellishly clunky, confusing and oftentimes looks ugly (because i have no idea how to fix the brush settings, so it's on constant-MS-paint-esque mode). as stnmaren says, its truly "a punishment" lmao