lolwut
...Anyway, I also find editing to be difficult but rewarding, It feels great to finally finish with a chapter and leave it alone for a while...y'know, before inevitably returning to carve huge chunks out of it right before posting. >:9
My process is basically Write->Rewrite->Rewrite->Rewrite(^n)->Time to post/draw; rewrite time is up!
I don't worry much about grammar or spelling; that stuff comes naturally to me. It's all about getting from point A to point B, punching up the jokes and the drama, making it all make sense. Going over the lines with a fine-toothed comb until I'm SURE it does.
Although the editing process often feels like it will never end, I don't subscribe to the idea that you can always improve on a script. Sometimes well enough should truly be left alone; sometimes a scene has just a simple job to do and it gets it done. At some point, your edits just start making things 'different', not 'better' by any objective measure.
If nothing else, that idea implies that the longer you work on a piece of writing, the better it will get, and that's a dangerous path to go down. u_u The chances that any single story actually deserves 10 years of your life are very slim; you gotta know when to stop.