24-70mm
for u

16-35 is UWA

for the price of a 24-70, you can get a 28 1.8G, 50mm 1.8G and 85mm 1.8G, and still have rm1k left in hand

lazy carry three lens then buy all rounder lens then.  

i duno, i GG all the time...no $$ change newer body haha 

never try different body shoot same thing see how big the difference image is.... 

AiS lenses are too obvious. Yes, the 17-55mm f/2.8 lenses are still being sold. There are ones where people have bought since as far back as year 2004 when it first came out ! Very obvious that they are out of warranty but the ones bought as late as 2 or 3 years ago would be the ones that would be questionable by Nikon as warranty card looks identical to the one now.
Yup. Those with older warranty cards sure cannot tipu. But I believe the warranty card as far as 2 or 3 years ago is the same as the one now if I'm not wrong. Those are the lenses that are in question and which Nikon wants to filter out.

Not to imply that vearn27's warranty claim is bogus but from another point of view, Nikon does this to protect themselves.
300mm would still look small. Unless you can crop crop crop... 
Distortions are not too bad. Unavoidable on 35mm format. You just need to know how to avoid it.

If you need something wider and better performing that the 16-35mm f/4, the 14-24mm f/2.8 is the one. Cons? No VR and ND / CP filter system for it is very costly.

Anyway, if you have to choose only one, the 24-70mm f/2.8 is a good all rounder lens.
One lens to rule them all !!! 

Seriously, it would depend on the type of photography you're into. Event photography, the zoom would be number one. Studio portraiture / product photography / landscape photography would benefit having primes. The 24-70mm f/2.8 would be slightly inferior compared to the primes in the same focal length (especially corners) but flexibility wise, no prime can beat it. If you're willing to sacrifice a little bit of quality for speed and flexibility, the 24-70mm f/2.8 is the one to choose.
While this sounds too funny and almost like a joke, it's very true indeed.
Nothing is ideal and perfect. Speed in exchange of sacrificing a little bit of quality is sometimes worth the gamble...
Ideally, the 14-24mm f/2.8 AND 24-70mm f/2.8.

Since you only can have one at the moment, get the 24-70mm f/2.8.

I would suggest keeping your DX as a 2nd body and mount a decent lens like the Sigma 10-20 to cover the extreme wide angles. The 24-70mm f/2.8 (or 70-200mm f/2.8 depending on the occasion) goes on the FX body.
Yup.
What's the problem with age? I still use lenses that are more than 10 years old.

Anyway, f/1.4 lenses sound very nice to have and shoot with but for events and concerts, your subjects need to be very still to be able to get a shot in focus under low light. DoF is so thin. With bodies delivering crazy high ISOs at fantastic quality, you should not be worried about shooting with f/2.8 lenses.
When their website was still new, I tried to register but somehow the application did not go through. Gave up after a few tries. 

I can tell you wide open the Sigma it is not pin sharp. If you want sharp wide open, the Nikon AF-S 14-24mm f/2.8 is the one you should get. Even then, the 14-24mm f/2.8 is sharp in the centre and not sharp in the corners at f/2.8 wide open due to the wide curvature of the glass i.e. like what you mentioned DoF is not the same in the centre and in the corner. What more for a lens that is more than twice cheaper !

Anyway, why do you need a lens sharp wide open? Wide angle lenses for landscapes are usually stopped down to get DoF. By then, any erros due tot he lens curvature is taken care by the DoF from stopping down.

I'll post an example below that I took a while back and without looking at the EXIF, could you tell the difference between the two disregarding the slight WB and FoV difference? Stop down enough and you could not tell a difference at a glance.



Like I mentioned above, the best wide angle lens also suffer from slightly soft corners. More obvious if you shoot on a 36MP FX body. Not so obvious on the smaller MP D700/D3/D3s FX sensor and certainly not at all on a crop sensor because only the centre portion of the lens is used.

It is so difficult to get corner performance sharp like the centre. That is why good wide angle lenses cost almost the same as their tele counter part because it's more difficult to make a wide angle than a tele. This is why DX cropped sensors were made initially when digital cameras came out because DX sensors concentrates the centre part of the sensor and disregards the corner areas of the sensors which is most difficult to get correct.
There are custom made filters. Just that they cost a BOMB ! 
The Tokina makes decent pics. If you're taking landscape pics and stopping down the lens, it is cheaper to go the DX route.

If you need a wide angle that is also a f/2.8 for shooting dark night clubbing scenes, the 14-24mm f/2.8 should be the one.
LOL, nice to have but most of the time it is not nice to the pocket. 

Thanks for the insight.. cause i never really used an UWA before and most of the things i "know" are from reading and some things, you really need to experience it.. reading is not enuff.. that's why asked your opinions.. i only read that remarks and not sure if that is really a deal breaker in actual usage..
yep~ i tend to stop down unless i require more light or i really needed to get rid of distracting backgrounds, but i guess for UWA, i wun really need to use DOF to get rid of distracting background, cuz it's just difficult to do so i guess.. hahaha.. oraite~ i'll check out the sigma again

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Added on June 6, 2012, 2:21 pm
i did a quick read.. haven't finish reading alot of stuffs, but i noticed that the lens has no VR.. for me it's quite a deal breaker.. not sure if you are ok without the VR.. without VR, at 135mm, you need quite high shutter speed to take decent pictures and at f/5.6, i think you might be lacking in light.. not sure if it's really applicable