What Camera should I go for next?

I have a Canon 450D (Rebel Xsi) and a Nikon D90.

The camera's I'm looking at are the Canon 5D Mk II and Canon 7D or the Nikon D700.

Also I like the look of the 550D.

I'm planning to sell the D90 to put some money towards the other camera but can't decide which option to go for. I'm looking to set up my own photography business and the camera would mainly be used for portraits.

What do you guys think is the best option?

Added (1). Jens… I do prefer Canon but I had to buy a Nikon (the D90) for work and I did have a go with the D700 and really liked it.

I'm looking to set up my own business by next summer and looking to upgrade my camera before then.

Added (2). As far as lenses go I have a canon EF 50mm f/1.8 a Nikkor AF 50mm f/1.8 and a canon 18-55mm EFs

BUY NIKON D7000! Its just GREAT!

Just wondering… Why aren't you sticking to one brand?

Anyway, for portraits a nice full frame camera will have an advantage, as it enables you to use shallower depth of field than it would be possible with a crop sensor camera.

Are you sure that it's a good idea to enter a very competitive field if you can't even decide which tools would be suitable for the job yet?

Nikon D700

Here is something to consider.

If you have a collection of Canon EF-S lenses for your XSi they will be useless if you buy the 5D Mark II. The 5D Mark II is only compatible with Canon's EF lenses. Attempting to use an EF-S lens on the 5D will result in damage to the mirror.

If you have a collection of Nikon DX format lenses for your D90 they can be used on the D700 in the "crop" mode. In other words, the DX format lens on the FX format body will give you an image the same size as you get on your D90. Lenses from the D700 are fully compatible with your D90.

I'm going to offer the suggestion that you already have perfectly good cameras and that buying new ones is premature at best and a waste of money at worst. How about accessorizing with a new lens or other equipment?

Sell your Nikon gear. And buy the following.

- Canon 7D - good all round camera. It's fast, got a good VF and has wireless transmitter.
- Canon 70-200mm f4L IS - I prefer the f4L to the 2.8L because unless you're a professional bodybuilder you have to get the IS version of the 2.8.
- Sigma 30mm f1.4 DC (you won't be able to afford the Canon 35 1.4L).
- Two Metz 48AF1 flashgun, and some flash stands, and brolly brackets and brollies.

All this gear should set you back around £2000-3000, and that will be what you need if you're going to be able to deal with most eventualities.

Here is a really radical idea.

Learn how to use the equipment you have already and how to take proper images with them.

As you have two different brands of Dslr then it is obvious that you don't know that much about photography but like to believe that the better (or more expensive/upto date) the camera then the more "professional" you are.

The cameras you have are fine for all but the most specialist shooting and with the right lighting and lenses would be perfectly fine for use for portraits etc.

Either of the ones you've got are fine for portraits. I would stick with the D90 and get some better glass instead. When shooting portraits, lighting is critical - invest the money you would have spent of some off camera lighting & modifiers.
You won't see a lot of benefit of a full frame camera with portraits.

You seem to be under the impression that you will get better images out of 'better' gear, without realising that what you have is fine.
Get a 2-3 light setup (preferably with battery packs for optional location work), radio triggers, stands umbrellas, softboxes, etc & learn how to light - a far better investment.