Poznan or Wroclaw

I say Wroclaw, it's a lovely city with fascinating architecture.

toss a coin-though Poznan's bisnis fame mainly seems to come from its 2/year MESSE=trade-fair, when that is on, avoid that town. WR does have a tiny bit more of market+old buildings but by sure its no Krakow or even close to. If you are in fact looking for a more short-time but Polish small town experience-go to Bydgocscz, Torun and around.

I know lots of people like Poznan, but IMO it just has a little old town (which is nothing on Krakow or even Warsaw), and not really much else to look at - especially mid winter. There are a few things around there, depending on what you like to do (like the Bronze Age village at Biskupin) but at the moment transport is infrequent because it's so off season. Wroclaw is lovely, and there is a day walking tour that the tourist office has that takes in the old square, new square and islands, but I don't know it's all that special or all THAT different from Krakow.

Exactly how long do you have? Because it's only about 2 hours on the train between the two and you could easily do one as a day trip from the other.

Wroclaw is indeed lovely but there is enough there to keep you going for about a day and a half...

Gdansk-Gdynia-Sopot with a visit to Malbork might suit you better if you have 3 days or so...

While Poznan is definitely worth a visit, if I had to choose b/w the two I'd go to Wroclaw. The historic area just seemed bigger and the enormous & beautiful main square has a 'wow' factor on par with Krakow's (but unique).

Another vote for Gdansk! But I have not been to Poznan.

Thanks guys! Yes Gdansk is lovely - I was there last summer. That's why I want to try something new this time. Looks like people favour Wroclaw over Poznan. But what is there to see and do in Wroclaw (apart from the obvisous old town square)?

Wroclaw gets my vote too - pretty, good sights, lively nightlife in student season. There's enough for 1-2 days of wandering around: several huge Gothic churches, the renovated synagogue with a new exhibition, the Unesco-listed centennial hall (modernist architecture), a huge panorama painting (of the Raclawica battle) and a museum with Gothic treasures. I think the newly renovated city museum in an old palace will open soon too. You can do trips to nearby Swidnica and it's Unesco-listed (and rather amazing) wooden Peace Church, to the mountains at Sklarska Poreba, or to the underground Nazi factory complexes southwest of Walbrzych.
Poznan is still nice too, and has a superior cafe scene IMHO, but has a smaller feel to it; Gniezno and Lednica (may be closed in Jan/Feb) and the steam train depot at Wolstyn (perhaps combined with a walk in Wielkopolska national park) are nice daytrips.
Both cities have to work harder to attract foreigners than Warsaw and Krakow and perhaps that's why they have much better tourist info offices; do visit them online and in person to get information and walking maps.

Wroclaw itself is the best part (the architecture), and here are some recommended sites:

Ostrow Tumski - Island where city began

Museum of Architecture - bldg itself is cool; stained glass, gargoyles, old tile stoves, etc. had a special exhibit of modern italian product design when I visited that alone was worth it

University - swordsman statue out front; ceremonial hall inside is truly impressive

Cathedral of St. John the Baptist

The Panorama (Tapestry) - sadly closed when I visited, everyone in W. will tell you to see it

Nat'l Museum (of Art) - b/c I love art; lots of the usual old religious carvings & paintings, but the modern collection is excellent and fascinating after you've seen one too many carved Madonnas

Hala Targowa - large indoor market hall with the usual produce, baked stuff, butcher,s etc. and a very popular little restaurant just inside the door - pop w/students from univ and babushkas alike... fun to just wander through.

Have fun.
ps--different feel from Krakow, though of course there are similarities (i.e. univ students everywhere, architecture) etc.)
pps--"Le Bistrot Parisien" is a cool little spot for a crepe w/side of Polish-style French atmosphere; there's a Coffee Planet right on the rynek that's a great place to sit & watch world walk by the big windows--good coffee & artsy feel inside; but v. popular