Looking for a Fisheye lens for my Nikon D3100?

I'm going to rent a fisheye lens for my Nikon d3100.
Which lens is good for the d3100?
I saw that nikon has their own fisheye lens but which one is better?
or are their other better ones. I'm going to take photos at a family event.

Nikon's fisheye lenses are of course are excellent lenses, but when it comes to fisheyes, unless they are being used for a scientific or industrial purpose, a much less expensive fisheye lens like the 6.5 mm Opteka or 8 mm Rokinon

http://www.amazon.com/...B002KMAWO0

http://www.amazon.com/...002LTWDSK/