Originally Posted by
billp
There's no sense in going all the way to Charlottenburg or to Hauptbahnhof with the bus. I would take the TXL bus to nearby Beusselstrasse or the X9 or 109 to Jungfernheide and then take the Ring S-Bahn (S41) CLOCKWISE (the train indicator may say Gesundbrunnen or Storkower Str.) to OSTKREUZ. Change there to the S9 to Schönefeld.
Another option - maybe faster - is the X9/109 to Bahnhof Zoo (the berlin-airport.de website says it's only 19 minutes but I don't believe it) and then the Airport Express regional train to Schönefeld (32 minutes). The disadvantage with this routing is that the Airport Express runs only every half hour, so you could end up cooling your heels at zoo for a long time. The S-Bahns run every few minutes, so they may be somewhat slower (more stations), but you're moving not standing.
Excuse me, but have you ever used the FULL Berlin public transit system? Every change takes at least five to twelve minutes. So better avoid extra changes. That is what I said in my original reply and I stick to that, especially if you are not used to the S-Bahns and U-Bahns. And the OP isn't.
Giving the advice of taking the 109 into Zoo shows that you never used at least this connection. The 109 goes all the way up Kurfürstendamm after calling at Charlottenburg station. So you give the advice NOT to get off the slow bus and on the fast rail but stay on that bus for another 15 to 20 minutes?
Taking the TXL in Zoo is the advice other people have given too, so it is old news. 20 minutes is a realistic travel time. But you have to change at Zoo station which can be confusing. And apparently it makes no real sense: You can take the 109 to Charlottenburg and get the very same trains (airport express and S-Bahn) there without being forced into the heart of what used to be West-Berlin.
Sorry, but pls. refrain from giving advice based on websites. There are people on this board, me included, using the system every week. And believe me: There is no connection I have not already tried.