Trouble deciding on new Nikon D5100 Lens?

Okay so I have a Nikon D5100 and I have the 18-55mm kit lens alongside the 70-300mm Sigma and 35mm Nikkor lens.

I'm thinking of adding a new LENS to my collection and Have been looking at Ultra Wide angle lens and fisheyes… Now I will be wanting to take "selfies" and I want to take photos of rooms in houses and get capture the most amount of the room as possible.

ALSO very important is that the lens should be good in LOW LIGHT.

I was looking at Tokina 11-18mm lens and also the sigma 10-20 mm lens.

Does anybody have any recommendations for advice?

I would prefer the Tokina. However if low light use was important I wouldn't mind focusing manually with one of these:
http://www.bhphotovideo.com/...f_2_8.html

I have the Tokina 11-16mm f/2.8 for my Nikon D90. I have found it very sharp and all the wide angle I'll ever need. (Anything wider probably would be a fisheye anyway.) Highly recommended.

The best low light lenses will have a large aperture of at least f/2.8, and they'll have some kind of image stabilization or vibration reduction (VR) as Nikon likes to call it.

No one, including Nikon, makes an ultra-wide DX lens with any kind of stabilization.
Nikon does not make any DX ultra-wide zooms with an f/2.8 aperture.
Tokina is the only one that makes a DX ultra-wide zooms with an f/2.8 aperture: http://www.bhphotovideo.com/...4109120025

If you don't mind using an FX lens on a DX body, the Tamron 15-30 has both an f/2.8 aperture and vibration reduction. This would be the best low-light lens, providing that it's 22mm (35mm equivalent) is wide enough for your needs.

This kind of situation is why the Sony mirrorless cameras and the DSLRs from Pentax have such an advantage. They both have in-body image stabilization which moves the sensor and not the lens. Therefore any lens that fits will be stabilized too. You may want to consider dumping Nikon for Sony or Pentax.

To see how these lenses compare, go to photozone.de

Tokina makes 11-16 and 11-20mm f/2.8 lenses. They don't make an 11-18. Both will auto focus on your camera. If you go for the 11-16, be sure it's the version that will autofocus on your camera as there's an older version that is only AF, not AF-S. The 104° field of view on these lenses mean you can get a whole room in from wall to wall and keep straight lines straight (after correcting for easy to correct distortion). Perfect for real estate shooting.

Both the Tokina 11-16 and 11-20 are sharp lenses. I've tested out the 11-20 and it is a very sharp lens even wide open at f/2.8. Distortion is negligible at 20mm and easily correctable at 11mm. Being f/2.8 lenses, they are perfect for indoor shots.

With a DSLR body plus the substantial weight of this lens (1.3 lbs - it's well built and meant to survive) will make casual selfies cumbersome unless you use a tripod. Plus, being wide angle will tempt you to shoot at close distances which will accentuate perspective distortion giving you a big schnoz. Of course, I did meet a guy who loved shooting faces within half a metre because he loved distorting facial features with his ultra wide lens.

If LOW LIGHT is your concern, get the lowest f/numbered fisheye you can afford.