Warsaw is a big and booming capital, but it still doesn’t get as much attention from most travelers as does Krakow, for several main reasons. Business travelers dominate, so hotel prices can feel high during the midweek. Still, Warsaw is a beautiful city that is very friendly and easy for tourists.
There are plenty of decent hotels in Warsaw, with most of the better budget options in and around the Old Town area. A large batch of international-style hotels are going up there and in other districts, so the choice will continue to widen.
The main attractions and general transportation in Warsaw remain quite inexpensive by European standards. If you go to Krakow you’ll likely be told to skip Warsaw, but that would be a mistake. This city is underrated and far more charming than you’d probably expect.