If I were to pick one I'd go with slice of life - if that slice of life is really more of a light daily humor strip than a "cute people that don't do anything" strip. Those are by far the most marketable across the web, and the lack of necessary investment to enjoy them makes them accessible to a wide audience. My slice of life interludes generally perform much better than my drama or action pages.
The caveat is that for slice of life humor, you actually have to be funny and original, or else it won't go anywhere. Action comic fans seem to like things to be as tropey as possible, you can just mix popular current battle comics in a blender and those fans seem to prefer it. So if your art is passable rather than great and your writing is mediocre, action battle will probably find more success.
