No watermarks would be a major plus in my opinion; kinda shows you went a bit out of your way to find something worth entering. Sometimes you just can't help a watermark (minus editing it out obviously), but I think entries from other major gore sites should come much lower on the points system.
The bread and butter categories for most shock sites are murder, suicide, accident, and tourture. They cover a wide range of possible videos for peepz to enter into. If a video is good but has no place, then maybe a miscellaneous category would be in order. This is the first attempt at a contest, so don't stress out too much over it @Libertas.