At 100% crop it should be obvious that a 41 MP Lumia 1020 is crisper than a 20 MP Xperia Z1. What Sony is touting however is low light performance. For instance, look at the following.
The reason professional photographers think megapixels are overhyped is because despite increasing pixel resolution, it makes great sacrifices in low light performance. In this test, the 1020 can't even beat it's predecessor, the 925. It isn't even in the same class as the Xperia Z1.
Having more megapixels in the 1020 means you can have much higher resolution pictures, but at the same time you sacrifice tremendous low light performance. Both smartphones have the best cameras on the market. The choice is simply between either a higher resolution than the already stupendously high 20 megapixels, or phenomenally better low light performance.
For reference, 20MP is equivalent to 5248 x 3936 resolution. If you're computer monitor is 1080p, you wouldn't be able to see the differences even if you made it fullscreen.
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