As I already said above:
I'm at the GH Berlin several times per year for business. I know it very well.
I would never use a suite upgrade in this property as the suites are not worth it. For me personally, especially when going for 1-2 people, I prefer the Deluxe room, as it feels more spacious (no separate loving room though).
The grand view suite, which I booked cash last time to see it, is surely a nice room but the regular suites are not so great that I would want to stay there.