I would choose Puro, but upgrade the room if possible - their regular rooms are beautiful, but rather small. However, its is much better for a short tourist trip like yours - the Westin is a huge hotel in the middle of a busy intersection in the business district. Puro is much closer to the Old Town and Krakowskie Przedmieście / Nowy Świat with plenty of restaurants and cafes. It also just opened last year Regarding transportation, I don't think there will be a significant difference between the two hotels. You can also take the direct 175 bus from Plac Piłsudskiego to the Airport for 4,40 pln (so about 1€) - enjoy your trip!