Image quality

These two cameras have the same sensor size.  So the one with fewer megapixels will have larger pixels (and larger pixels allows for better image quality).  pixel-size at snapsort.com

Megapixels have nothing to do with image quality. For the most part MP just mean how large you can make the photo, a 16 MP is more than enough, unless you plan on taking photos for billboards.  

Give a detaileI currently have the A65, there are more differences between the A57 and the A65 besides the pixel count.  The A57 is the upgrade from the A55, brought up to second generation sensor and SLT mirror guts, while the A65 is the baby brother to the A77, which is the uprade and conversion of the old A700 to the SLT line.  If you are looking for a simpler to use camera, then go with the A57, if you are looking for something that is a little faster, a little more advanced, a higher pixel count (you can crop a higher pixel count with the same results of an A57, remember mid format cameras are using 30M - 80M pixels not because they plsn on cropping but because they want the detail in their pictures- that being said, the ability to take advantage of the increased pixels takes practice)