Because I'm a huge nerd I'mma expand on what Puckit said.
Listen, there's a lot more to taking a good picture of your cock than the camera itself, but since you asked:
Megapixels have become increasingly less relevant since the standard hit 8. A 14 megapixel point-and-shoot camera will not get as high-quality a picture as a 10 megapixel full-frame DSLR. Why? Sensor size. The real size that matters when it comes to digital photography is sensor size. A bigger sensor will capture more light. Period. And, in the end, photography is about capturing light.
With a smaller sensor you can have a smaller lens and a more compact camera; however, images come out muddier - and smaller sensors have a harder time capturing a good image under poorer lighting, like the indoor lighting which most guys use to take cock pics. So the closer to credit-card-size your camera is, the harder it will be to get a really nice snap of your dick - generally speaking. Why "generally speaking"?
1) Sometimes smaller cameras are made with better parts, so it's really just a rule of thumb. But mainly 2) A good photographer can figure out how to get a great picture out of almost any camera. In fact, there are photographers who have made their careers getting great pictures out of crummy point-and-shoot cameras.
How you treat the subject matter is more important than any technical specification. People debate whether there are any absolute rules in photography, but what I just repeated (cause it sure isn't my original idea) it at the top of the candidate list.
It's getting away from the question you posed (so I'll try to be brief), but to get really great pictures of your cock you need a well-lit room, you need to experiment (which it sounds like you're already doing), and you may want to dig around a photography site, such as
About Photography - Photography Lessons, Forums, Contests, and News.