Hilton at Warsaw is pretty good. Located at the center? of the city and there’s a light rail station right downstairs(Warsaw uprising museum and ghetto are both very close too!) I highly recommend the bar right across the street. If you go out from the back side of the lobby, go straight to the first crossing. There’s a very good bakery if you walk left at the crossing but the staff there don’t speak English. There are many highly rated restaurants in the area. If you walk straight there’s a Soviet-themed restaurant called the red hog and their menu is hilarious. If you take the light rail line 1 you can go to local malls and stuff(but malls are boring anyways they are all the same around the world).
For Krakow, if you are planning to go to Auschwitz-Birkenau find a local tour company. Or you will have to wait in a long line for nongroup visitors. There’s a flight from Warsaw to Krakow every morning and evening. If you have a tight schedule like me you can choose to fly to Krakow in the morning and fly back to Warsaw at night. You will be able to see Auschwitz and the city within a day but you won’t have enough time for salt mine.