I am thinking of Poznań, Lublin, Krosno and Białsko-Biała.
I've never really heard of the universities in Krosno and Bielsko-Biala (not to say they're bad, I just haven't heard)
I've heard different things about the Catholic university in Lublin (and the town itself).
Poznan is known as having the best language programs in Poland (though less so for Polish for foreigners) though from what I hear they've gotten better in recent years. I haven't heard anything bad about the Polish for Polish students program.
Poznan is generally more used to dealing with foreigners and it's also a good base for travel (easy to Warsaw, Berlin though connections to Krakow aren't good). dephiandomine is right about bad housing though (and the local housing market is not cheap).
Poznan also has a Hungarian dept (I don't know if that's an attraction or not).