Under Penn is pretty gloomy, but I did a stint at the construction of the Gotham Tower and my work area overlooked the SunnySide Yards. Quite a bit of activity, Amtrak, LIRR, and NJT, lots of "looping" and the added bonus of the portal where tunneling debris brought up from the ESA project was loaded on trucks and carted away. That area is pretty bright with good visibility
If someone could partner with the developer of the Whole Paycheck *Cough Cough* I mean Whole Foods right there on Roosevelt Road in Chicago would be an amazing place. You would get every long distance train passing (yes even the Builder coming from the Yards), plus all of the corridor trains (including in the early morning late evening the Hiawatha going to/from the yard). Then on top of that you get the Metra BNSF, Southwest Service, and the Heritage Corridor. If you moved the camera to CP Lumber you would get even greater variety because you would have some freights as well. I believe someone maintains a webcam in Chicago on the Burlington line right at Union Station where all the trains wye unless they have power on both ends such as the Wolverine/Blue Water.