Isn't the Samyang 14/2.8 a wide angle lens and not a fisheye?
Both WA and fisheye will give you nice skateboarding pics, but different. Try borrowing before you buy to help you make up your mind. My choice would be fisheye of 15-16mm so that you will get a full picture and not just a circle like the 8mm ones will give you (I use my 16mm a lot more than my 8mm).
Now and then there is a cheap fisheye so just keep looking.