I am traveling to Italy for work and decided to stay back for 5 days. I am flying back from Vienna because i was getting cheapest airfare from Vienna. Now my dilemma is if i should stay in vienna for 5 days or if i should go to Berlin for those 3 days. I am in mid 20s and i believe Berlin will be a great option due the nightlife and other things but i am apprehensive about the cold weather there.Does it get really bad in Berlin i.e. sleet, slow etc? or is Vienna the same. Also, if i stay in Vienna for 5 days, will i be able to find good nightlife and other things during the day to keep myself occupied?

Berlin is usually drier and colder, but that time of year is usually still more in between fall and winter so any weather you mentioned would be within the norm in either location. Usually snow and ice are more common from Jan to Feb than in Dec.

Re. nightlife you should not unterestimate Vienna. Aside from its image of waltzes and wine and "old" architecture, the city is a very vibrant European capital. I would say that more people here prefer the traditional forms of entertainment so you hardly find any mentioning of evening activities beyond the opera and heurigen/ wine establishments.
This site of Vienna's tourist info may be a good starting point, though, if you prefer to experience a more "wilder" Vienna. Or check Lonely Planet's thorntree forum
http://www.wien.info/en/lifestyle-scene/nightlife

As you are going to be in Vienna anyway, I'd stick with it, but do you have to leave italy so quickly? why not spend a couple of days there before making for Vienna?

Yes i have to fly back home from Vienna.. As far as Italy goes, i have been there as a tourist before.. So if i go to berlin , i will take a return flight from Vienna to berlin..

yes, i got that, but didn't realise you'd seen to Italy before [all of it?]

I'd still stick with Vienna - lots of music, christmas markets, nice cafes, wonderful museums - and you could do a day trip to Bratislava if you got bored.

Climate will be the same in Berlin and Vienna. If you are in the 20ies, I strongly recommend Berlin not just for nightlife.

Weather in both cities is likely to be similar. They both have real winters and it's likely to be quite chilly to cold - and while it's a little early for snow - you can easily get sleet, ice or snow in either place - in fact, in almost any place north of the Alps.

For young, trendy nightlife I think Berlin is better.

And as long as you have proper winter clothes neither one should be uncomfortable. Just be sure you have warm boots with non-skid clothes.

How about also the university town of Graz? Vienna is lovely, too. I am sure you will find nightlife everywhere through other forums.

Thanks everyone for your suggestions. I have decided to visit berlin for 3 of those 5 days.