It's snowed a lot the last couple days, and should continue to do so this week. So conditions are rapidly improving.
If your plan is driving to the airport Monday morning, then yes traffic will be an issue (although Sunday afternoon can be a nightmare as well as people drive back from the mountains). So I get your point of staying as close in to Munich as possible. As you plan to ski Sunday, you also need to consider the weekend crowds in your decision.
Of the places you mentioned, forget Oberaudorf. It's a small beginners hill. Spitzensee is similar to Sudelfeld (were you say you have skied before) but a little more interesting. However it also gets much more crowded than Sudelfeld as it is ever so slightly closer to Munich.
You don't say what kind of skiing you like, but you did mention off piste skiing, so if conditions are good I would highly recommend Wendelstein (the other mountain in Bayrischzell). It's a real gem, and it is never ever crowded. You can also stay in Brannenberg instead of Bayrischzell, which is easier to access from the autobahn (although that means not staying in Bayrischzell, which would be a pity).
Garmisch is generally rammed on the weekend, but if you go in that direction Lermoos just on the Austrian side of the border is great for a day and usually much less crowded. You could ski there for the day and stay the night in Garmisch.
Kampenwand in Aschau would also be a good option.
If you want to ski off piste exclusively, Laber in Oberammergau and Karwendel in Mittenwald are epic in the right conditions. Both towns are also very charming.
I guess the "one bar in town" in Bayrischzell is the Sport Alm? There is another next to the train station now that is also great. Incredibly friendly owner and nice group of regulars.
Honestly, since you will be staying overnight on a Sunday and therefore should not have any problems getting accommodation, I would wait until the last minute and chose based on conditions. No new show: Lermoos or Sudelfeld. Powder: Wendelstein, Kampenwand, Laber or Karwendel. I personally would not ski Spitzensee or Garmisch on a Sunday.