Wanted to post this since everyone else's experience and advice has been so helpful -- I believe I've found my solution!
Phoenix proper, 4.5 miles from the towers
HR10-250 DirecTV receiver
Zenith Silver Sensor
Stucco 2 story house
I first tried an RCA ANT 145, on clearance at Target, since I was so close I didn't think it would be worth spending any more on an antenna. However, from what I've gathered, the HR10-250 is easily overloaded by a strong signal, which is what I believe I get, being so close. Also, the RCA was omni-directional, and with all the fences and houses around I'm guessing I get a ton of multipath as well. Long story short, I could get a good signal on all the networks that matter to me (ABC, CBS, NBC, FOX, PBS), but I would always have to choose at least one station that came in unreliably. Not a big deal, unless you need to have the capability to record on any channel at any time (can't be there to babysit reception!) So, the RCA not only overloaded the receiver with a strong signal, but it also gave it way too many choices. Based on my need for directionality, no need for VHF, and no need for amplification, I purchased a Silver Sensor yesterday and I think I'm set. I was most worried about the effect my chicken-wire-wrapped stucco house would have on an indoor antenna, but it doesn't seem to be a problem. However, I think I'm picking up secondary signals, which is fine, since they're constant for all stations between 85-90 (according to the HR10). I have the antenna oriented at a 90 degree angle to the exterior wall only an inch away, between the wall and the 50 inch plasma TV. I'm assuming secondary signals because never before have all the signals been more tightly grouped in terms of strength -- I can get better reception than that if I point directly at the towers, which I can see out a window less than 2 feet from the TV. However, pointing directly at the towers didn't yield a satisfactory signal on all channels for some reason, possibly because it was too strong? It seems like the best strategy is to start pointing directly at the towers (from antennaweb), finding your weakest station, then adjusting until that station is the strongest. It's likely there will still be an adequate signal for other stations, since this antenna gets such a good signal. I'm guessing the only adjustments others in Phoenix would have to make would be either attenuation or amplification, because all the towers are located in the same location for most.