UWA dilema

Im looking at purchasing a sigma UWA my choices are the 8-16mm or one of the two 10-20

I know that they all have their pros and cons. Just would like some input as to what other peopled picked and why they picked one over the other.

Im really enticed at the 8mm end of the 8-16 but the constant 3.5 would be nice too (although i think when shooting wide don't most stop down to f/8-f/11 or maybe i am remember wrong), i have zero experience with a wide angle lens but i have plenty of places i can see one being very useful around here.

either choice will leave me with no gap or even some over lap with lenses as i am also picking up the sigma 17-50 os and that sorta makes me want to lean a little more into the 8-16 but again just looking for others opinions/experience before i pull the trigger and pick one of these up.

thanks for any input

for landscape, you will likely stop down to f8. but for many other applications you wont (video, interiors, group shots). the 8-16 is optically very good, and superwide, and fun to use. I say go for it.

i will be using which ever of the lenses for landscapes and cityscapes, but i don't see myself using it much indoors (but stranger things have happened), i wish i knew how to add a poll!

Is there a reason why your not interested in the Canon 10-22mm? It's only a few hundred more than the Sigma 10-20mm.

The two higher priced sigmas are at the top of my budget and the 8-16 is really enticing.

Either the 8-16 or the older 10-20. Keep in mind, the 8-16 won't take screw-in filters, which are kind of important for landscape.

Unless you really want the extra 2mm on the 8-16, I'd just take the older 10-20. The slighter faster aperture on the 10-20 3.5 isn't much of an advantage: DOF is pretty deep at such wide angles so you don't gain much DOF control; you'll likely be stopping down anyway; even if you do use it wide open, you'll gain just a bit over a stop of shutter speed, and with wide angles, you don't need great shutter speeds anyway.

The usual suspects in UWA topics are the Canon 10-22, Tokina 11-16, Sigma 10-20 (both versions) and 8-16. The Tokina 12-24 comes up less, although it's also a fantastic lens. The Tamron 10-24 has left a sour impression in some reviews it seems, so I hardly ever see it recommended. A shame, since I've seen more than decent results from it, and it's easily the cheapest with the biggest range.

When I was shooting crop, I was really in love with my 11-16, which still holds my recommendation as it's the sharpest but also fantastic build quality. The only downside (flare) might well be fixed in the MkII that was just announced. You might want to wait for early reviews on that. Otherwise, you can't possibly go wrong with any of the ones I mentioned as they are all good - provided that you inform yourself well in regards to things like the filter size or lack of filter options.
If you want to keep the option of buying used open, I'd just see what's available for a good price.

Another thing to consider WRT the Sigma 10-20 f3.5..it takes 82mm filters: expensive and not shared with many other lenses. **TweakMDS' post reminded me of this**

You mention landscapes and cityscapes. To me that says GND filters and CPLs. Both of which are a massive pain to mount on the 8-16. Combined with the fact that for both applications you'll be stopping down to ~f8-11, save yourself some money and go for the 10-20 4-5.6, which conveniently has a smaller filter thread than the 3.5 thus saving you even more money in the long run.