It's is a bit difficult in comparing fisheye and rectilinear lenses, as the focal length is not really an effective approach. The best approach is to use Angle of View. The 10-17 has an AoV of 180 to 100 degrees wide. The 12-24 has an AoV of 100 to 60 degrees wide. So, essentially the two lenses complement each other, rather than compete.
The 10-17 fisheye is less fishey at 17 than at 10, but its still a fisheye. You can use various utilities to defish the images, but depending on the perspective it is at time less effective that what you may want. The fisheye is great for extremely wide views. These views are obtained at the expense of the center which is essentially "push back", so that the additional view is able to be pulled in around the edges (top, bottom, and each side).
The rectilinears are great at keeping straight lines - straight, especially square things square.
Which type to get - really depends on your intended usage. The fisheye is really a specialty lens. Having said that, some of my best images were taken with it. For instance, things in motion where you need a really wiiiiideeee shot - the fisheye. The fisheye is great where you would need to stitch with a rectilinear.
You can stitch with both types and the results are great. The colors and contrast are excellent with both types also.
If you have not tried stitching, I would encourage you to give it a try. Just downloads a copy of Microsoft Ice for free.
The zooms are much more versatile than the primes. I have over the years acquired the 10-17, 12-24 and 8-16. The 8-16 is a wonderful lens. I picked it up so that I could shoot the square rigged "tall ships", single shot from the top of the mast to the waterline. I also wanted all the rigging lines to be straight. The 12-24 just was not wide enough for this - otherwise, I would have been satisfied with it.
I too would go rectilinear before the fisheye (but I acquired mine the other way around).