Łódź definitely the least beautiful.
Łódż has its own atmosphere; a late C19th planned city on a grid pattern.
Also very popular with filmmakers; David Lynch has talked about its unique and special feeling, plus of course there's the famous film school and studios. Good theatre there too.
Gdynia is at least handy for Gdańsk. The other two are country towns; may as well be in Lincolnshire in terms of attitude and much more...