We will be taking a taxi from our hotel to the train station for an ICE to Munich. I see I can start at the Hauptbanhoft (Main train station) or Sudkreuz. Assuming my hotel is between them, which would be better, the biggest or a smaller station?
Actually, if you are close to an S-Bahn station. you can buy your ticket from that station and it will include the connection at the most convenient station. Might save you a taxi ride. What hotel are you at?
Sheraton Berlin Grand Hotel Esplande
You could pick up an S-Bahn or Regional train at Potsdamer Platz station and take the next train to Sudkreuz. Shorter cab ride to Potsdamer Platz. You will have to use the cross-over bridge at Sudkreuz to change platforms.
The hauptbahnhof is worth seeing if you have the time - https://www.youtube.com/watch?v=7a5JMcDPCfE
Hauptbahnhof, hands down.
It looks like most of the trans from Berlin to Munich spend 9 minutes at the Hbf and only 2 minutes loading at Südkreuz, if that makes any difference to you.