I would use XnView myself, in your situation. It has batch processing and you can save the processing "chain" to a file, so next time it is there for you to load and run with a few mouseclicks.
Regarding your problem: it may make sense to resize the images to the specific screen width or height of your reading device. I myself usually resize the images so that the width is equal to my reader's height (bebook NEO) and then read the comic with my reader in landscape position. This method suits me well when the comic has an a4 or letter format.
For comics that already have proportions that resemble my reader (manga for instance), I resize the image so that the width is equal to my readers width, and read the comic with the reader in portrait position.
(I do my processing with a (customized) manga2pdf-v4.5.2 Linux-script I found on this very forum, but you don't have Linux)