How much do megapixels matter?

I'm stuck between the canon rebel t4i and the nikon d3200. The nikon has 24 megapixels, whilst the t4i has 18. I have a retina display macbook pro and i will be wanting to take pictures up to 2880x1800 in size. Can the t4i handle this? I like everything else about the t4i. I will be shooting pictures of nature and also taking video. Can you explain how many megapixels i need and what they do? Will i be able to take 2880x1800 pics with the t4i? With the d3200? All feedback is appreciated; thanks so much in advance.

They matter, but not as much as you may think when you read the adverts for digital cameras

What matters most is the size of the sensor and how well the cameras electronics utilize those pixels

http://www.kenrockwell.com/...mpmyth.htm

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

In the end, you have to decide.

Visit a proper camera shop and hold both in your hands.

Remember, whichever camera system you buy, you will be using it for a couple of decades

Either of those cameras have excellent optics, so that shouldn't enter in your decision of which to buy. There are other cameras that the optics are so bad as to result in the picture/film to be useless. That happens with cheaper cell phone cameras. People tend to say " well they have the same amount of megaxils, so they must be same quality," but that isn't so.