I will travel to Vienna and Salzburg for Christmas and will finish in Salzburg on December 26. Now, I have to choose whether I want to depart from Munich or Vienna (ticket does not allow me to depart from Salzburg). I will be travelling by train from Salzburg to either one of the cities and then go to the airport. Which one is more convenient? And how do I do it?

By train, Munich is 2 hours away, Vienna is 3.5 hours away.
At the main train stations in both cities, it is easy to get to the airport. In Munich, you can take the S-Bahn. In Vienna, you can take U3 to Wien Mitte (7 stops), then S7 to the Airport (8 stops).
Given the choice, I would go to Munich since it is closer and only one SBahn to take after arrival at the main train station.

The best way to the airport in Munich is with the Lufthansa bus from themain station. Handling luggage is easier because the suitcases go under the bus in a locked compartment and the bus makes one stop enroute to the airport.

I have tried both ways, and I take the bus everytime now. Managing luggage on the S bahn is a pain if you have much of it.

The bus makes a couple of stops at the airport for T1 and T2. Itis important to know which terminal you need.

Thanks to both of you. It seems that it's better to choose to depart from Munich.

The bus service sounds good and easy. Bob, is that the main station in Munich that you're talking about? How can I book it?

I have never booked the bus in advance. It runs frequently, 3 times an hour as I recall. I do not know the exact location at the train station because I take it at the Nordfriedhof location which is the one stop the bus makes enroute to the airport.

If the freeway is jammed, as it was when I left this past September 19, the bus company radios the driver with alternate instructions. (It was Oktoberfest, and the traffic pouring into town looked like rush hour even though it was Sunday.) I understand that the bus has 7 alternative routes it can take.

There is a good web site in English with contact information that will answer most of your questions.
I could not find a diagram of just where the bus stop is at the main train station. But there are information desks at the train station, and someone there will direct you to the right spot. I have never had a problem finding someone around the train station who spoke English.

I don't know if the Bavarians pride themselves on knowing English, but I find that they are quite willing to speak English if they know any. Some of them will surprise you with their extensive knowledge of English. I got a surprise when our waitress in a small restaurant turned out to be quite a chatterbox, in English. We acted friendly and even though I can speak a little German, she got rolling in English and was obviously enjoying herself!!

And for Heaven's sakes, don't say insulting remarks about Bavaria or Germans with the idea that the cab driver does not know what you are saying. We have found several cab drivers who were fluent in English.

If you take the train from Munich to Salzburg, chances are it will stop at Ostbahnhof. You can get the S8 from there to the airport and save the time and trouble of going to Hauptbahnhof.

There can be problems flying out of Vienna to the US. Lufthansa occasionally will cancel their afternoon flights and "fold" them into the morning departures, most of which connect later through Munich or Frankfurt anyway. There are more nonstops from Germany than from Austria.

My parents did this on Tuesday & used Munich for departure. Everything went smoothly for them.