university of warsaw or sgh warsaw school of economics
Both are good, both have decent student life. SGH certainly has more contacts with Polish companies which would be useful if you decide to stay on after your studies, however long-term UW could be a better bet. Why not have a look at fora for current and former students of both. There you will get a feel of what people who have studied at both institutions are saying about the current situation.
Good luck, and I hope you have a great time in Poland.