My cover is pretty much just a cropped version of issue 5's cover. I think it should be representative of your comic, and give the reader a good idea of what they are in for when they read your comic. My banner pretty generically shows the two main characters, and that they are serious business, and its a fantasy setting. 
I've seen some comics with a title logo, some without. My title is pretty clear on the page already, so I don't bother to messy up the image. Although I notice that sometimes one of the characters gets cropped off if the window is too small, so I might flip the image someday... XD