Klára is lovely, helpful (she's even made some quite exhaustive manuals for "using" the flat: )) and most flexible. The place is only a few minutes from Charles Bridge, and a few more from a Tesco. Restaurants, bars, pubs are also only a stone's throw from the flat.
The place itself is stylish, cosy, well-equipped, so if you don't mind a few steps (within the flat as well), it's probably one of the best choices in Prague :)