Hi there I am hesitating between these DLC: Southeastern High Speed: London St Pancras - Faversham Route Add-On/Great Western Express Route Add-On/Great Western Express Route Add-On or Hauptstrecke München - Augsburg Route Add-On thank you for your attention
I would go with Munich - Augsburg, but this is what I like. If you are in doubt, I suggest you take a look at the release videos that Dovetail made before each release in Youtube. You can watch each one of them and decide if you like what you are seeing or not.
Hauptstrecke München - Augsburg hands down in my opinion . Even more so if you have other German content due to layers
Munchen-Augsburg is great once you have many or all of the other German routes, because of the layering of rolling stock; but by itself it's rather empty and lifeless, and the gameplay is basically driving back and forth over the same stretch of largely straight track. GWE shares that problem, but you do get a greater variety of services out of the box. Don't have SEHS but it does appear to have two very different faces: the Javelin run along HS1, and then the slower bit in Kent.