I don't know what Olaf is talking about regarding architecture, because both cities are more or less in the same category.
Regarding infrastructure he is right, untill next year when some important works will be finished including highway bypass of Wroclaw. But I suppose public transport still will be a little better in Poznan.
Well it all depends on your goals... From leisure perspective it goes like this:
- if you prefer to be closer to lakes, Baltic Sea, Warsaw, Gdansk and Berlin then Poznan is for you
- if you prefer to be closer to mountains, Polish and Czechs(preferably...) ski resorts, Cracow, Praque and well Berlin, then Wroclaw is for you
Would Poles consider Lwow or Wilno to be more attractive cities then Poznan or Wroclaw?
Not really, most of Poles have never been to Lwow and Wilno...