which to buy 10.5mm or 10-24mm zoom?

Get the 10-24mm/f3.5-4.5 AF-S DX; it is a far more general-purpose lens.

I have the 10.5mm fisheye. It is a highly specialized lens for occasional use. If you really need one, you should know that by heart and shouldn't be asking about it. The fact that you asked is a good indication that you don't need one.

I also have the earlier 12-24mm/f4 AF-S DX. I use that a lot more often then the fisheye.

As Shun says. Fisheye lenses are a one-trick pony (so far I have four of them, link), but ultrawides (as they are called. link) are rectilinear lenses that can be very useful for all kinds of photographs. Indoors, landscapes....

The 10.5 fisheye is fun to use in very rare circumstances and of not much use in most situations. Weird analysis but that's the way I feel about mine. As Shun says, if you have to ask you probably really don't want/need one. The perfect lens to try as a weekend rental before you spend the money for a purchase.

Agreed. The fisheye produces a very specific look that can quickly become tiresome if over-used. A rectilinear ultra-wide (like Nikon's 10-24, or its various counterparts from Tokina and Sigma) is wildly more useful in all sorts of situations. It's the difference (especially since you mentioned landscapes and architecture) between a highly stylized look, and a more straight-up capture of what's in front of the camera. Though, at 10mm, you can produce images with very striking perspective effects.

I've already got a 10-20, which I really like on a DX body. But there are at least half a dozen lenses I'd purchase before I'd put money into a fisheye. I suppose that if I shot skateboard/snowboard action stuff all day, I'd change my tune ... but I don't! You won't regret the UW zoom.

I owned the 10.5mm DX fisheye, and while it is an outstanding lens, it was only used for less than 5% of my photos. I bought the 10-24mm DX last year and have loved it ever since, even though it too is used for less than 20% of my photos. It is by far the more usable lens of the two, and I like it better than the Tokina 12-24 and Sigma 10-20 that I had before it. The Nikon 10-24mm DX is a keeper for sure.

I am sure that I use the fisheye for well less than 1% of my overall images. Sometimes I shoot a wedding or party and I'll capture a few images with it. That was precisely what I had expected before I bought it.

Thanks all for your responses they are most appreciated. I WANT the ultra-wide look artistically. I know that BOTH lenses can be CORRECTED to rectilinear (close to it, or better). So disregarding all comments as to usability, OPTICALLY does any one favor one lens over the other for sharpness, contrast, color, etc. I am asking this as I have never seen these two lenses compared to each other. Also, if I use my 105 macro for portraits, which I do, if I step 5 feet closer it is an 85mm, and if I step 5 feet backwards it is a 150mm; a "walking zoom lens." At 10mm or 10.5mm which is the better optically? Second, the "coverage" of the 10 to 24 is that really that much of a plus to buy a zoom over a prime in the ultra-wide range. Again thanks.

optically, the prime is sharper. so if you really want a fish get a fish.

but here's another reason to get the 10-24: it most likely is better than your kit lens from 18-24, meaning less distortion.

according to photozone, the 10-24 has almost no distortion at 18mm and very little at 24mm: http://photozone.de/nikon--nikkor-aps-c-lens-tests/443-nikkor_1024_3545?start=1

the 18-135, otoh, has a considerable amount of distortion at 18mm: (link)

that said, there are very few zooms which are as sharp as primes, and the 10.5mm fisheye has a reputation for being one of nikon's sharpest lenses. it also has a fast aperture of 2.8, meaning that if you're willing to de-fish in post, you have an ultrawide which will be very good in low-light situations where the 10-24 wouldn't be due to the variable aperture.

personally, i would probably get the 10-24 if i didnt already have an ultrawide. in general, having a wide zoom range is preferable for landscape, while the 10.5 is extremely wide and may be too wide for some general landscape use. however, a fisheye is well-suited to skateboard or live band shots, or for getting really really close to exaggerate the perspective.

I had the 10.5mm for a while. It was fun sometimes and pretty sharp.

The correction programs come with their own flaws. The image quality around the edges is bad, or at least was with Nikon NX.