I prefer simple designs. Should be unique and identifiable. If the design is too realistic it may just look like a picture of a turtle which doesn't work as a mascot. People need to see it and know it is referencing me.
If possible provide at least two color variations on it so I can see what it'd look like. Black and white isn't the only color I'd like to use. The ben brown is a great example of a simple logo but I also really like cartoon logos as well like: