Actual megapixel count is just a number...almost. There are many important factors. Aperture size, pixel size, censor size, etc. The Galaxy S4 and LG G2 have 13mp cameras. The new Sonys have a 20.7mp. But the iPhones have "only" an 8mp, yet they often produce the best photos in "blind" comparisons, which proves that it's not only the physical aspects of the camera, but the software as well.
And then there's the "other" hardware as well. Some phones, like the LGs and the Nexus 5, also feature optical image stabilization, which reduce shake, meaning lower ISOs, less noise, and better low-light performance (at least in theory). Newer cell phone SoC (system on chip) processors have more and more features and capabilities. For example, the brand-new Qualqumm Snapdragon 801 that we'll see in the Galaxy S5 and Sony Z2 has better camera capabilities than the previous (but still top-of-the-line) 800, which is more capable than the older 600, etc. And of course, the same holds true for Apple's processors, Mediatek, and in-house processors such as Samsung's Exynos.
All the above is why you can't simply go by megapixel count alone.
And of course, lighting is a huge aspect with any photography. The best camera in the world won't take good knife pics if you're doing it in my dimly lit apartment.
Right now the best camera phones are the LG G2, Samsung S4/Note 3 (and, presumably, the upcoming S5), the Sony Xperia Z1 (and upcoming Z2), the Google (LG) Nexus 5, the iPhone 5S, and the various Nokia Lumias. The king of them all is the 1020, which has a 41mp camera and a xenon flash. Some others have "only" a 20mp camera with LED flash. The 928 has a xenon flash, but "only" 8.7mp. Honestly, you can't really go wrong with any of these phones, as far as the cameras go. It'd be hard to say that any single one is "better" overall, in every aspect (except probably the Lumia 1020), since they all have different features, be it software or hardware, that give them advantages in different areas over another.
Another thing to keep in mind is that many cell phones have a 16:9 picture ratio as the default, because the picture will fit the screen. However, this crops the picture from its actual ratio of 4:3, which results in lower MP. Make sure you set your camera to the highest MP at 4:3 ratio to take the most detailed pictures. Any cropping/reduction can be done later.