I moved out of the house in 1992 but my dad still insist I make his chocolate chip cookies for him. After much searching these are the ones we deemed "best". Soft and chewy but with a lightly crisp outer layer. If you don't want the crispness, substitute more butter for the shortening.
I have found that you need to follow the directions *exactly* to get the best cookies. Not using real butter or all brown sugar, not beating the eggs in one at a time, not baking them at a higher temp than the "traditional" recipe, all make a difference in the end result.
I have also found that Land o' Lake butter makes a better cookie than some generic brand butter. Don't let the butter sit out too long. It needs to soften but if it sits until the moisture starts to separate from the butter, it is too soft and it will affect the resulting cookies. If that happens, refrigerate the dough for about an hour to help them not spread as much. It also helps to use the mixer on the dough in between batches going into the oven. It helps keep the dough from starting to separate if it is a warm day.
Another thing I've learned is you have to make sure there is plenty of circulation in your oven. When I moved, my cookies started turning out flat again. I finally realized that my oven was smaller at the new house and when I switched to smaller cookie sheets, my cookies turned out perfectly!