I have the kit lens, the 16-45, the 12-24 and the 10-17. I like wide angle and landscapes. Each of the lenses has their place and their own particular strengths. You really can not go by the focal length alone (especially with the 10-17), you have to go by the field of view figures in order to understand the differences between the lenses.
By far the 12-24 is the sharpest, especially at f8, however it is a larger lens physically - larger than the 16-45, and has a massive front lens. I have read postings of others indicating that it can be though of as a group of primes rolled into one. Its not as sharp as each (all) of the individual primes (14, 15, 20, 21 and 24) that are available, however its very close. You also have to look at the center sharpness as well as the sharpness at the edges. I find little distortion with the 12-24 (detectable). If you plan to use filters - especially a polarizer, look for a very thin filter lens, so as to not add to any vignetting. Also, at these wide angles, you also need a very good filter optically, so that you will not add any more distortion. With the large front lens (77mm), the filters are large - and expensive.
The 10-17 I too like very much. That said, you have to understand what it will do and how it will do it. As everyone has indicated, its a fish eye, even at 17mm - its just not that pronounced as it is at 10mm. At 17mm the field of view is 100 degrees wide. Take a look at the field of view at 17mm with the 16-45, its different, much narrower - in the low 80 degrees (probably around 81 to 82 degrees). So the fish eye distortion is still there, it is just less apparent. On man made objects, the distortions are more pronounced than with natural objects - in that the eye knows what to expect with man made or essentially square objects (or things with a lot of straight lines). With objects in nature, trees, etc. (or things with curves already), it is more difficult to detect the distortions. With the 10-17, you have to understand, how the extra field of view is achieved - the center is pushed back, such that the additional field of view from the edges are able to be brought into the frame - which essentially produces the curvature in the images. With that understand, you can select your views and frame them appropriately. One thing with the 10-17 is the ability to get close - as in "Macro" close - inches. You can get really close to very LARGE objects, and get them all in the frame - its incredible.
hope that helps...