Take Szczecin on border, sleep and work there then drive/take train 1 and 1/2 hour to Berlin, Germany for fun.
Or better still just rent a flat in Berlin. No need to come to miserable Poland at all then :)
If you are under 28, then Warsaw, Poznan, Torun, Gdansk should be OK. If you're over 28 then forget it. The night life is very much geared to the very young. All the older folk sit at home and do absolutely nothing but watch TV and drink, so you'll have a very difficult time meeting new friends.
If over 28, then Kraków is a far, far better idea, as life doesn't end at 28 (probably more like 35). Can't say much about Wroclaw, but I think it's on the up and perhaps even slightly more Westernized now than Krakow.
If you're over 35 and still unmarried then I think the only thing for it is to go to Berlin (or basically just don't come to Poland.)