Which DSLR, either Nikon or Canon, is good for using in low light surroundings?

I own a Canon EOS 1100D. I always shoot 100 ISO and want to. I have problems shooting portraits inside. I use my house light from the ceiling and with the light from my window, it is not even dark. It's quite bright actually. I always have to have my shutter speed on long exposure just to get the light showing. Even 1/60 shutter speed, and my image is quite dark. I tried everything.

Added (1). I'm using an 18-55mm lens that comes with the 1100D.

Added (2). Just an addition to the question, I was thinking about buying the 600D, how is the low lighting situations with this DSLR?

I just bought a Canon T2i and it works very well in low light settings

Getting a different camera will not cure a basic problem that is easily cured by a bit of knowledge

Spend some time researching for yourself

http://www.dxomark.com/...ase_sports

This link shows you how various cameras perform in low light.

As you can see, your 1100D comes in at 84th when it comes to low light performance

Spend some time on this site learning how to balance ISO, shutter speed and lens aperture.

http://camerasim.com/camera-simulator/

You are trying to ignore the exposure triangle (probably without knowing it exists) and you think that a different camera will somehow magically make it disappear. Read up on exposure. The problem isn't the camera; it's you.

Sounds like your using Manual Mode, you can't just set values in the exposure triangle (ISO, Aperture and Shutter Speed) you would like to set, interiors are darker than you think.

Use Aperture Priority (A or Av) set the Aperture you want, the ISO you want and half press the shutter, the camera will tell you what Shutter Speed it needs to set for a close to correct exposure.

Currently we have a really bright sunny day here, my office has a south facing window and light coloured walls, Sunlight is streaming in, the room is as bright as it ever gets.

If I use my incident light meter, which measures the light falling onto the subject and I know to be accurate to 1/10th of a stop, in the bright light streaming through the window at 100 ISO and a Shutter Speed of 1/60th of a second I need to set my Aperture to f4 for a correct exposure. Go outside and the Aperture goes down to f11. If I sit at my desk, out of the direct Sunlight, and take a reading the Aperture needs to be opened to f2.8. Interiors are never as bright as you think.

Canon camera sensors are old technology, the newer Sony Exmore R sensors used by Nikon, Pentax, Olympus etc, and, of course, Sony are far more sensitive, only 25% of a Canon sensor's surface area is sensitive to light, on the Sony sensor it's 94%, this extra sensitivity makes them better and less noisy in low light.

Another point is that the lowest ISO setting is rarely the best for noise, usually a higher setting (200 or even 400) is often less noisy, it varies from individual sensor to sensor. Using my Pentax K5 I can shoot at an ISO of 1600 and still have zero noise even in low light, it's much less noisy than the K5 lowest ISO setting of 80.

I recommend canon T3i which is a best solution to your problem since it has ISO 100 - 6400 for shooting from bright to dim light and a very good shutter speed. Since you are already using a rebel your experience will aid to better photography with this model.

Canon T3i is a 18 MP CMOS Digital SLR Camera and DIGIC 4 Imaging with EF-S 18-55mm f/3.5-5.6 IS Lens. Here is a review from a professional photographer, i hope it will help your decision:

http://www.amazon.com/...9N74Y83IH/

Some of the major reasons to buy T3i are:
It has ISO 100 - 6400 for shooting from bright to dim light
T3i has great video Snapshot features for enhanced video shooting options
Vari-angle 3.0-inch Clear View LCD monitor (3:2) for shooting at high or low angles and 1, 040, 000-dot VGA with reflection reduction with a CMOS sensor with DIGIC 4 Image Processor for high image quality and speed