Options for upgrading from a D90 to a non DX-sensor camera?

My brother broke my D90 camera and I thought perhaps it would be a good opportunity to maybe go for an improvement from the D90 model. (Anything from Nikon or Canon would be great)

Well since you seem to want a full frame camera like the Nikon D600, at least all your existing lenses will still work with it.

I hope your brother 1) is paying to help you replace it and 2) you have learned NEVER to loan your camera to any one, even relatives.

That actual upgrade of the D90 would be the Nikon D7100

Here is how the D90, D7100 and full frame D600 sensor performances compare

http://www.dxomark.com/...nd3)/Nikon

As you can see, either the D7100 or D600 would be a huge improvement over the old D90

If you get an FX Nikon, any DX Nikon lenses you have could fit and work on the camera, but they would tend to be dark at the corners of the frame if shot in FX mode.

If you get an FX Canon, you would of course need Canon lenses, and they must be EF, not EF-S lenses.
If you go FX you will pay a price in money and weight for the kind of lenses you will need.

Nikon D600 or Canon 6D?
Here is some comparison
http://www.cameralabs.com/reviews/Canon_EOS_6D/verdict.shtml
The Nikon can have a little edge in detail capture. The Canon offers lighter weight and better low light autofocus. In a studio you can have an arsenal of perfect prime and professional lenses. If you are going to travel with the camera performance vs weight matters, so you want versatile zooms, but you still want FX's quality potential. I think Canon gains an advantage with its EF 24-105mm f4 lens that is reputed to be better than Nikon's 24-85mm f3.5-4.5 or its 24-120mm f4.

I recently upgraded from my D90 - which by the way is still a great camera.

I had the choice of the D600 (full frame) or D7100 (DX) camera.

http://www.amazon.com/...00BI9X7UC/

One thing you need to realize that with either camera, you need good lenses to match. Otherwise you are not going to get the performance you paid for with a standard kit lens.

The D600 is superior to the D7100 in low light capability - due to it's full frame sensor. However, the D7100, lacking an anti-aliasing filter has a slightly sharper photo capability.

At the time I bought the D7100, I had 10 lenses, 4 of which were DX lenses, which means I would have had to buy a few lenses if I had upgraded to the D600.

You can certainly use the 18-105mm lens that came with your D90 for the D7100 unless your brother broke that too. This lens is a DX lens though, so it will not work as well with the D600. The D600 will shift to DX mode, but at the expense of resolution (10Mp I think).

I ended up buying the D7100 body only and the Sigma 17-50mm f/2.8, which is a great lens - a lot better than the 18-105mm you have (although it does not have as much reach). The total cost of the D7100 body and Sigma lens was $1, 800 - $200 less than the D600 (body only), and about $700 less than a D600 with kit lens.

http://www.amazon.com/...003A6NU3U/

And you could spend that $700 for another great lens.

Thing is, when I upgraded to the Sigma 17-50mm, I gained low light capability. The low-light performance difference between the D600 and it's kit lens and D7100 with the Sigma is now about the same.

So the D7100 with the Sigma f/2.8 equalizes the low light capability of the D600 with the 24-85mm f/3.5~4.5 kit lens. Of course, you could upgrade the D600's kit lens to a f/2.8 and get that advantage back, but then you are spending another $500~$1.000.

So the matter really comes down to budget. You can get the D7100 with great image quality and with an upgraded lens, great low-light capability as well - for about half the price of the D600, especially when you consider lenses.