Wide angle lens

I'm looking at getting either a true fisheye lens or a wide angle lens, but I'm not really sure which one I should go for. The two lens I have picked out are the Canon EF 15mm f/2.8 Fisheye Wide Angle Lens and Canon EF-S 17-85MM f4-5.6 IS USM Standard Zoom Lens

The 15mm will give me sharper pictures and it is f/2.8, but it also has no zoom, which can be kind of handy, then again it gets rid of the wide angle if I zoom.

The main purpose I'm buying this lens for is to take pictures of BMX bikers and skateboarders.

I'm looking for suggestions for a different lens or any other feed back.

These are the two shots I got today, both are 28mm 1/5000sec f/3.5 on a 1.6 crop
http://files.travisperson.com/jpg/IMG_0030_small.jpg
http://files.travisperson.com/jpg/IMG_0064_small.jpg

Personally, I'd go with a prime lens. I think the optics are going to give you mo-better images. Plus, if it was me, I wouldn't want to have to change too many setting when doing live action, like this. That's what you'd have to do when you change focal lengths, you have to re-think the whole shot. I think it would slow you down.

Also, I'd want to drop below 4 on the f-stop.

Have you looked into any sort of tele-converters?

The fisheye is probably the most popular lens for doing any type of skate/snow/bmx work. If you're seriously interested in a wide angle, you may want to consider the EF-s 10-22 f/3.5-4.5.

The 15mm fisheye is a great lens. If you're looking for wide without the fisheye, go with the 14mm rectilinear - can't be beat.

There's really no comparison there. The 15mm is going to be a better bet hands down. Faster focusing and a much faster max aperture which you'll need if you get to shooting indoor parks. Personally, I end up using three different lenses when I shoot BMX: 16-35mm 2.8L MkII, 24-70 2.8L, and 70-200mm 2.8L. I much prefer zooms to primes just because of versatility, but unless you've got about $5,000 laying around for the three I noted you should grab the 15mm.