So far, the Connecticut state quarter is by far the best, in my opinion. The texture of the 'charter oak' against your thumb makes this quarter a pleasure to handle, and the intricacy of the design, makes it just about perfect. Many other quarters are totally uninspired, namely Massachusetts, who's state map, and generic 'revolutionary guy' really don't do much for me. If I made the rules for quarter design, I'd eliminate state maps, and require symbolism to be a bit more subtle.
The Best so far: CT, RI, MD, NH, VA
The Worst: MA, PA, GA, SC
Click here for a list of all (Vermont Looks Promising!)