Position 2 also seems to be the most successful historically. I can think of a number of examples from the Indian Wars alone, and if one factors in the Philippines and the Marine experience in the interwar period the number grows.

You do need a reserve, although I would contend that it doesn't have to be infantry per se. Cavalry/armor can fill the reaction force role to perfection, while depending on the terrain you can use airmobility to solve some of the speed problems (the Marines became quite good at this after 1969, and the First Cav had many successes as well). Of course these factors are heavily influenced by terrain (both natural and man-made), but to not have a reserve of some sort is to surrender the initiative, and that's never a good idea.