The camera does NOT matter. Many times I get asked if I should buy Nikon, Canon, this model or that model... what you should be asking is what kind of lenses you need for the type of photography you want to take. Yes, I'm talking here about DSLR cameras (more about point and shoot below). Spend less money in the body that has the features you are looking for, and spend the rest of your money in good lenses. A very good expensive camera with cheap lenses will deliver low quality photos; revert the order and you have a great combination.
When it comes to brand; it really doesn't matter either. Most photographers buy one brand over the other because they have some lenses already or they like the colors of the advertising. The reality is that all cameras these days can deliver great photographs if used with high quality lenses... so pick your brand and go buy a body that can get you good easy control over shutter speed, f-stops, ISO, white balance and has a decent photometer (which is not as important underwater as it is above the water). When it comes down to sensor size then you have to decide between Full Format (FX - sensor size equals to 35mm) or crop format (DX - which is 1.5x on a Nikon and 1.6x on a Canon). FX is much more expensive that DX and to me it does not make sense to spend the extra cash... I rather spend the difference in good lenses.
Interchangeable Lens Camera Nikon
Don't get caught in the Mega-pixel marketing campaign! More mega-pixels don't mean better photos. Better lenses means better photos; again: spend your money in good quality lenses and forget the mega-pixel and camera features scheme. Some of my favorites Nikon D3100, 5100, D7000 or Canon Rebel T3, T3i or 60D. Don't discard older cameras that are awesome like the Nikon D40 with a flash sync speed 1/500 which you can get on eBay cheap these days (same goes for older Canon).
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