It depends what you are looking for, a good place with local cuisine or international food, an elegant, posh place, old-fashoined style or modern, awarded with Michelin stars or not, etc.
Griechenbeisl is an overpriced tourist trap. Augustinerkeller is a so called City Heuriger, a Heurigen without the traditional garden or vineyard setting, for me not apropos at Christmas.
We liked Plachutta very much, especially because of the traditional boiled beef, widely unknown in US.
Anna Sacher would be my favorite, but it is a very elegant place, jacket and tie recommended.
Oberlaa is a good choice at noon, very good three-course lunch specials.
Silvio Nickol's place bears the highest awards in that list, rather expensive.
If you want to eat in a café, Landtmann would be my selection.
Read the homepages of the different places, maybe TripAdvisor ratings. It is very difficult to judge what may appeal to you.