Hi, I wanted to advise you to use the 12mpx mode always. In photography there is a point where past a certain amount of mpx adding more will not improve the quality of the picture if not worsen it in some cases.
For many companies producing even full frames the sweet spot is 12mpx which is quite the standard. I have never been a fan of the high mpx count being pushed by the chinese first and samsung then to make up marketing numbers which even if I hate it are what drives the sales of a smartphone.
At 108mpx you will have weaker processing, less light per pixel and also you will not get 9 times the detail since the image is compressed and there is a geometric rule in sensor semiconductor according to which if you increase the mpx amount on a given area you need to exponentially improve the quality at the semiconductor level to get a linear gain in detail.
I hope samsung engineer will be free to do a good sensor with less than 108mpx if the marketing team allows them too, unfortunately from the rumours about an internal quarrel it looks like that the management supports the marketing team who wants a 200mpx sensor on the next s device whereas the engineers wanted to get back to a more conservative and better lesser amount of pixels... let's hope for the best for the next galaxy S!