I really enjoy the ease of the eZy Watermark photos app for single photos. I am using a png file without background for my logo, which looks great and professional when applied to my work.
And it's excellent when you're in a hurry. You just make a photo, go to the app, select the photo, select the logo, then move and rescale your logo, and go to export. When your logo is already uploaded to the app, you're done within a minute.
I also like the batch option. Though in that case, all photos need to be sized and orientated the same way, and because the logo will be placed on the exact same spot with every photo, you need to make sure there aren't any objects in that area in the photo, or the logo might not be very visible. Of course, this depends on your logo. I guess, I'm missing the option to move the logo around within this badge mode.