PayPal (linked to my credit card as well) is #2 for me. Most of the time I use instant transfer services (there are quite a lot of them in Poland, integrated with most banks in the region). My favourite one is Blik (founded mainly by the biggest Polish bank PKO BP, but also supported by most of the others): you start a session, generate a one-time 6-digit code in your bank's mobile application, enter that on the payment site, confirm transfer information on your phone and it's done. I also use it to withdraw cash from ATMs and on some occasions have used it to help my friends pay in emergency situations (they've just called me, I've given them a code, they've entered that, I've confirmed et voila).