Technically there is no location more central to all the sights in Budapest than Deak Ferenc ter. You can reach everything but Buda in about 10 minutes from Deak Ferenc ter. It’s also very close to the two largest Christmas Markets.
Now for the downside. There are two sides of the street. The river side is tourist central and expensive and while beautiful and restored (District V) it lacks a lot of the character that Budapest is popular for. The opposite side of the street (District VI and VII), just isn’t very pretty, generally full of the cheaper tourists’ souvenir shops, etc.
Astoria is an interesting location. Not my favorite but if you stayed at the Astoria Hotel, that would be interesting, and you are on the 47/49 tram so getting around isn’t terrible. But my favorite place to stay in on or close to Andrassy ut.
There is a list of good hotels here and they are mostly on Andrassy ut. https://community.ricksteves.com/travel-forum/hungary/rs-forum-favorite-hotels-and-their-cost . That puts you on the M1 Metro line which goes to or connects to most every sight in town, including the largest Christmas Market. Andrassy ut is a beautiful area, is very "Hungarian" in character, lots to see and do in your free time, great wandering walking street.
I tend to get a bit overly ... well you know ... about hotel locations. Whereever you end up, it will be a great trip.