Prague & Budapest
Congratulations on your trip; the wife and I went there a year and a half ago and we loved both cities. Although there is blackjack to be found, I didn't play too much as there was too much to see and do to spend much time in smokey casinos.
The BJ rules in both cities are standard European rules; 6 deck, ENHO, etc., and penetration was 75% at the places I played (but I did not make a complete survey.) All of the casinos I saw were pretty small, and only had between 1 and 3 blackjack tables. As is also the practice in Europe, you have to show your passport to enter.
The general playing levels of the people in the casinos was slightly above what you'd see in the US, but still pretty poor. Nobody on the other side of the table seemed in the least bit bothered by my bet variations. If you know how to track shuffles you will like it as they didn't shuffle very carefully. I did not detect any cheating, but that doesn't mean that it didn't happen.
The other post mentioned the Las Vegas casino at the Hyatt - that one has a nice feature; they play in Hungarian currency in half the casino, and US dollars in the other half. This lets you play without currency exchange worries.
My general advice is to have fun and, as I noted above, there's a lot to these beautiful cities, so don't spend too much of your vacation in the casinos.