
If you like to see a variety of traffic Aachen isn't a bad place to be. Lots of passenger traffic and quite a few freights hauled by DBs own locomotives or a variety of private operators, including quite a few continental class 66 locos.
The station itself isn't very big, but both end of the platforms are clear, and when you get there you can quite quickly make a decision where to stand depending on the time of day and the angle of the sun. It is a through station so you are unlikely to miss anything regardless of which platform end you decide to stand on.
I would personally recommend one of the middle platforms either 5 or 6 as any freights tend to go through the center roads of the station, and on my visit quite a few came to a complete stand as they were halted by signals.
Due to the close proximity of the platforms to the tracks I would recommend a wide zoom, personally I used a 17-40mm and only swapped to a telephoto to capture trains coming under the bridge at the end of the station.
Recommended for a few hours if you are passing.