As with most Apple products I always say go with the best one you can afford. However, I have stopped buying the "s" models long ago. I now just buy the ever other year larger upgrade.
For me it just came down to the even pressure needed for key presses. Older. On-mechanical keyboards would often have varying levels of pressure needed. Sometimes when playing games my hand would get really sore trying to hold the bets down. Mechanical keyboards just feel much better on the...