Getting around Vienna next week advice

1. Your options include three different trains or bus:

Train: City Airport Train: Non-stop to Wien Mitte station (on the eastern edge of the centre), sky-high tourist-soaking fares. Ticket machines most visible at the airport station to try to persuade naive tourists it's the only option. Really not recommended.
Train: Inter-city or Railjet: Non-stop to Wien Hauptbahnhof (south of the centre, a little way out). Yes, you can use these trains with a normal rail ticket at lower fare than the CAT. Buy tickets from machines on the platform.
Train: S-Bahn: Slower stopping journey to Wien Mitte. Buy tickets from machines on the platform (same ticket as the inter-city)
Bus: Vienna Airport Lines: Various stops in city centre, more expensive than the S-Bahn or Inter-City train, cheaper than CAT, but may be more convenient if a stop is near where you are staying and you don't mind the possibility of traffic delays.

I’m vacationing in Vienna at present. I chose not to take the more expensive and slightly faster CAT train to town. Instead, I took the S-Bahn, which works just fine. When you exit the baggage claim area look for the red ÖBB counter on your right. You’ll need to buy a single €2.10 ticket to get from the airport into the regular city transit zone. From the S-Bahn train you can transfer easily to the UBahn to get to your hotel in the city center. The people at the ÖBB counter are very friendly and helpful and speak English. Ask about transit passes. You can buy a 72 hour transit pass, which is good for 72 clock hours (not just three calendar days). I know that there are reduced prices for individual tickets based on age, but can’t recall if that also applies to transit passes. I also bought a transit map for 3€, which shows all uses, streetcars and subway routes, day and night time, which was very helpful. At any rate, you’ll find Christmas markets everywhere and you will do best to use mass transit to go between, as the weather is likely to be cold and rainy. You mentioned a concert at St. stephen’s. There’s a Christmas market right there. Karlsplatz market is at the same stop as the opera, just a different subway exit and is, indeed charming. Another good one for kids is at the old general hospital (Altes AKH), reached by streetcars 43 and 44. Spittelberg has more food and wine and more crafty/less christmasy things but is very popular with locals. It’s a few blocks behind the Volkstheater stop. You can also find a market in front of the Kunsthistorisches Museum, not all that far from Spittelberg. You’ll like the market at the Rathaus, but there aren’t many locally made items there.

I also did the S-bahn to the U-bahn and it was easy and relatively inexpensive.

The RJ trains (RailJet) and S7 trains (S-Bahn) run alternating every 15 minutes. Just take the next train, the fare is the same, the ticket is also valid for the subway.

With an RJ alight at Wien Hbf (main station) and take the U1 subway (red line) to the very center.

With an S7 alight at Wien Mitte (center station) and take the U3 subway (orange line) to the very center.

Both U1 and U3 stop at St. Stephen's Square, underneath St. Stephen's Cathedral, right in the middle of the historic center.

Nevertheless, there may be a better option depending on the exact location of your hotel.

Do yourself a favor and take a pre-booked taxi from the airport to your hotel. It will cost about 32 Euro and will be like gold when you arrive. Money well spent, especially when you see the sign with your name on it! I have two kids and that’s what I do. Here’s a link - https://www.flughafentaxi-wien.at/en/

As noted above, the Altes AKH market is also special in addition to the ones you already list. Here’s a good article - https://www.viennawurstelstand.com/guide/your-ultimate-vienna-christmas-market-guide-8-of-our-favourites/
And another good article (scroll down and ignore the German) with an excellent map -
https://www.1000things.at/blog/mit-dem-1000things-u-bahn-plan-zu-den-schoensten-christkindlmaerkten-in-wien/

When at Stephansplatz, duck into Haas & Haas and ignore the market in the square which is new and tacky. That said, when you are in the center, you ohh and ahhh at the lights, not the markets! Walk down the Graben, Kohlmarkt and Rotenturmstrasse instead.

Emily, excellent advice once again. I will take the cab and we will have a wonderful time, thanks in a large part to your help!!

Emily, I just sent you a PM. Thank you again, we look so forward to being in Vienna and watching the look on my grandson's face!!