All central European cities have some things in common - Storming nightlife, beautiful women, cheap drinks and eats, high adrenaline activities

Each city is a bit different, as well. Here's how:

Budapest

A top summer party spot because of the high number of outdoor venues open in the summer. From pubs to clubs, Budapest does it outside.
The city is bigger than the average in the region and bit spread out. This is good and bad. Good because it offers many areas with many venues and a very low saturation of stag parties. This is bad because if you don't know where to go, you're far less likely to find the good spots.
Highlight activities - take a riverboat loaded with strippers and eat sushi from a living table on a relaxing tour down the river Danube. Trabant rally - old soviet era cars on tour to the country for a pub lunch.
Highlight venue - 4play lounge strip club - by far one of the best in the region. It's owned and managed by expats so you know it's got to be good.
Why NOT Budapest - there's no real old town center. If you want an easy to walk, beautiful old town center try Krakow.

Krakow

A beautiful town, lots of students, open-air performances in the many squares, and over four hundred pubs give Krakow a great vibe. The city is small enough that really any hotel, even outside the 'Planty', can be considered central and you can wander around tripping into bars and hot women. It's large enough to offer a wide range of venues.
Highlight activity - Pub crawl - not your same ol'. Krakow has a plethora of cool pubs, but considering all the underground venues, alleys, and back streets you need to know where to find them. Guides are definitely recommended.
Highlight venue - CK Brower pub for fresh brewed brew and Golonka - Ham hock - slow roasted to juicy and delicious perfection.
Why NOT Krakow - Given the city was home to the late JP II, it is somewhat conservative. Therefore the strip clubs lag a bit behind the rest of the region. If you like your strippies try Budapest.

Kiev

Kiev is an exotic city and home to quite possibly the most attractive women in Europe. Come here to see a quickly developing former soviet city before it all changes and the birds get fat.
Highlight activities - Vodka tasting followed by clubbing. Get warmed up for a night of clubbing in the proper Slavic spirit. Wear your shirts and try your hand at the exquisite Ukranian ladies.
Why not Kiev - It's still a very expensive place to hold a weekend away. If the guys are on different budgets consider a different venue. But then again… The women!!!

Warsaw

An up and coming stag destination, which up to now was mostly visited for business purposes, Warsaw features great activities and a very surprisingly beautiful old town. It also has a thriving nightlife with loads of good clubs. This is a cosmopolitan city with diverse cuisine, music and entertainment.
Highlight activity - Rickshaw races through downtown. Fasten your seat belts, this could be a bumpy ride.
Highlight venues - Any after-hours pierogie stand downtown. Beats a kebab anytime.
Sophia strip club - The only choice downtown and one of the best in the region.
Why NOT Warsaw - This is a big spread out city. For a smaller easier to get around town try Krakow.