That's what I'm looking at right now, as it happens. Last time I was in Berlin, I stayed near Nollendorfplatz, but as I wanted to pick up my race number from Tempelhof, I got the U-Bahn from Jungfernheide to Platz de Luftbruecke.

This time, because I'm arriving early, my priority is to get to Alex to drop my bag off, then to tootle around Berlin in the afternoon to my heart's content.

Looking at an U-Bahn map, it looks like the X9 follows the route of the U7 part of the way from Jakob-Kaiser-Platz to Wilmersdorferstrasse. Would it not be as quick for me to go that way to Charlottenburg and then S-Bahn to Alex?

I don't mind a bus, to be fair, but I have a greater sense of making progress on a train.