the aps-13 is generally considered the best directional fm antenna available to the home user at a somewhat reasonable cost. but, for a high-performance antenna on a budget, consider the winegard hd6065. it is at least as good as the aps9a (if not better?) at half the price of the aps9a.
yes, you will need a rotor if you are wanting to get stations in different directions, & yes, it's possible to receive a signal off the back of one of these directional yagi's, so if you have a really strong station directly behind you when you're trying to pick up a weak station in front of you, look for an antenna w/the best front-to-back ratio. and, this is one of the few situations where an antenna tuner like the md signal sleuth may actually be of some benefit. re: the st-2 whip antenna, i and most other fm fanatics who have tried one have found that a $3 wire dipole almost *always* works better, but the dipole, like a directional yagi, also needs to be oriented for best results for a particular station.
re: lead wire, in theory 300 ohm twin lead works best, but in reality it does not. its lower signal loss is almost never realized, due to its susceptibility to interference from adjacent objects, (even its support brackets), movement, & poor weather resistance. rg-6 coax is usually the best choice. avoid rg-59 - too much signal loss. for really long runs, you may wanna consider rg-11, but it's usually not necessary.
doug s.