I guess it all depends on personal style! I love the 18S because the one I scored is perfectly puffy, yummy and perfect - I like the "bigger" pebbles/grain because it is like the double classic flaps (small, medium etc.). Growing up, dreaming of chanel, I only ever saw the classic flaps and therefore got very used to this size of caviar grain. Therfore, the current 18B small pebbles REALLY irritate me, they look like proper tiny caviar bits/sand - and I hate fish, and caviar for that matter
. I did not even know they make different type of caviar graining though so I guess by pure coincidence, I just got lucky with scoring mine the way I liked it.
I do see why people talk about preference when it comes to the shine, too. I did and do not like the matte ones because to me, in person, they looked plastic-y.. I like shiny leather. Its still a far cry from looking like patent, more like a lambskin thats been loved and has patina. I love that sheen..
that said; i can totaly relate why some would always pick matte over shiny or small grain over big grain. Its really all about what you prefer to go with your style and clothing etc.