Down size the 20mp to 6-7mp and then compare. That's how you have to do it to be fair. Sony is currently the leader in sensor manufacturering.
Seriously - the question should be what's the best 5x8 a camera can produce? 8mp should be sufficient, and more has little to do with improved quality of the photo (unless you are going to zoom and crop)
But it we are talking viewing on a 50" plasma, or perhaps a nice wall print...12mp? But is anyone that serious taking their photos without a DSLR?
It's kind of like the HD display debate - are you really going to watch a lot of tv/movies on your phone with a magnifying glass?