I think you mean Prague or Barcelona, either city is a lot of fun.  Which country to visit will really depend on what you want to do.

I whant to see something from the city (sightseeing). And Nightlife.

I would vote for Barcelona.

Yes i think i’ll go to Barcelona. Did someone have expirience Amsterdam?

If you base the trip on sight seeing alone, Prague is probably the better choice.  In the recent years Prague - city of 1,000 spires, has become one of the most touristed cities in the world because of its amazing old town square, charles bridge, and Prague castle.  It has a very medevil feel and some of the buildings are nearly 1,000 years old.  It also has some of the worlds best beer and a descent nightlife (depending on your preference). 
 
Barcelona gets a whole lot of tourists also.  Why?  Probably because Barcelona is the first thing that comes to mind when you think of Spain.  Why?  I have no idea.  Sights in Barcelona are not so intense and more on the modern side, but what sticks out more in my mind is the ambiance of the city.  Its very relaxed and friendly, even on mild winter days people stroll leasurely up and down the streets smileing and laughing (outside of a bar, Czechs are much the opposite). 

I’ve been to Prague, Barcelona and Amsterdam.  Don’t go to Amsterdam for a week, 2-3 days in enough.  Between Barcelona and Prague, it’s a tough choice.  I loved both, but I think I would go with Prague.  And it’s cheaper, so that’s always good.

 
I concur, plus Prague offers it all – beautiful architecture, interesting & deep history, excellent beer, food/accomodation is still dirt cheap, excellent nightlife, etc. 
 
Barca is a cool city too, but it depends on what you’re looking for really.  I liked Barcelona, but nothing about it blew me away or anything.