If you're visiting Western Europe, definitely check out cities such as Rome, Florence, Barcelona, Paris, Amsterdam, and other major cities of Europe. Their party scene is vibrant but welcoming. I got a copy of Party Earth's entertainment guide just recently and I found it especially helpful in terms of planning what to wear and what to expect from bars and clubs within those cities. They even provide reviews for the hottest social venues within those cities, pretty awesome. Check it out!
Well in general, Germany is also a nice place to stay. It is not that cold...We do have also winters with temperatures between 10 degree and - 15...It is indeed very different. If you'd like to party a lot and meet nice girls It is been told that the best party people and most beautiful girls do live in eastern Germany, such as Leipzig, Dresden, Berlin, ... All those three are well-know for a lot of students - so especially over the weekends you're gonna have many many parties... Out of experiences I can tell that in Dresden are a couple of discos where don't have to pay entrance and the prices for the drinks are okay...And as a nice side effect the city of Dresden is in general worth it to be seen.
The chances are, London and Amsterdam will also be freezing that time of year too.
You want warm in January, then it has to be Southern Spain, Malta, Gibraltar or the very Southern tip of Italy. You'll still need warm clothes at night though - most of the time.
Go to Eastern Europe......girls are the hottiest in the world