OK, the results are in of the unofficial Factory/Stubby antenna real world analysis.
I'll start off by describing the area where I tested today. I live in central Indiana about 30 miles east of Indianapolis. We have very minor rolling hills with patches of woods of several acres spaced 1/2 -2 miles apart. It's a perfect fall day with a slight breeze and clear blue skies. I parked my truck in the open to get away from misc. interferance that seems to occur around neighborhoods and concentrated power distribution systems.
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The stubby antenna I have been using since day one is the AntennaMastRus 6-3/4" copper coil for Ford Super Duty. It's not just a metal wire covered in plastic. It's an internal copper coil, thus mimicking, the quarter wavelength of the OEM mast as close as possible for it's size.
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First I quickly discovered with the OEM antenna that it was going to be hard to make specific station comparisons because there were way more than I expected and probably 95% were strong enough to enjoy listening to. If a station didn't come in perfectly clear I didn't include it in the results. So the results are just a quantity of stations with similar sound quality.
So to cut to the chase, here are my results:
OEM - It was able to clearly pick up AM stations as far away as Chicago, Nashville and Cincinnati. I counted a total of 39 strong AM stations reaching over 300 miles, and a whopping 59 very strong FM stations in a radius of about 80 miles. This included both analogue and digital broadcasts. Both AM and FM stations were equally strong from the lowest frequency to the highest. If I wasn't looking at the display I could not have distinguished where on the frequency range the station was transmitting.
Stubby - I counted a total of 9 AM stations and 55 FM stations, again both analogue and digital. Obviously AM took a big hit, but surprisingly, the three furthest stations still came in pretty strong with a little bit of white noise mixed in. As for FM stations, I think I got a good sounding signal on almost an identical list of analogue stations and totally lost of few of the digital stations.
Now a few caveats to my "scientific" test. I was running my test sitting stationary in a very open area. Driving between obstacles and land formations and the like would probably reduce the number of stations I would have included in the results. But I'm confident the reduction in stations would have been nearly equal for both antennas and would be more an indication of signal strength than quality of reception by the antenna.
So, my conclusion, at least for this particular stubby antenna, is that it performs far better at least where I live than many have indicated their experiences were with these type after market antennas in the areas they live in. Honestly for me the difference was almost negligible, especially as I tend to save a few favorite stations on the presets and stick to those primarily. I do listen to OTA radio occasionally, both AM and FM and for my needs the 6-3/4" AntennaMastRus, made in Wisconsin, works perfectly.
Now to address a few of the previous comments in the thread. As you can see I don't live where there are parking garages so I really have no need for a "feeler whip" mounted on the truck. And If I had the choice to park in a public garage, I wouldn't even consider entering if the clearance was marked less than 8 feet.
Oh, and for whoever commented regarding effectiveness regarding size and shape, I did notice when installing that my stubby had a slight bend causing it to tilt ever so slightly to the passenger side.

PS: I did entertain myself by removing the antennas and testing without any mast. Zero AM stations could be picked up at all and surprisingly, I did pick up one FM analogue station very strong and clear that is located 80 miles west in Crawfordsville, Indiana. I don't know how many watts they are transmitting but they are really punching that station out there. Probably wouldn't want to live close to the transmitting antenna.