Hello Devryimax,
Defining nice is difficult without more information, for example I met some young Italians that were unhappy staying in a nice quiet part of Bratislava as there was nothing open at night in walking distance so that had to get a tram or a trolley bus into the central part of town. There are others that I have spoken to that consider a nice area the part of the city that is nearest the forest as they like the walks and the serenity, this would not be a nice area for the previously mentioned young Italians!
If you are referring to nice mid range areas based on accommodation costs then perhaps the best way to understand what is on offer is to look at the property rent or sales section of the online English local newspaper called Spectator.sme.sk
Please update your post for this topic with a better description of what you consider to be nice and not nice as then we will have a better understanding of how to answer you.
Good luck.
