While more details are listed for each specific region, this page is here to offer a general overview.
Note that the results of the 2005 census with comparisons to the 1995 census can be found here as a PDF. There are also other doucments at the more generic URL. The documents are in Spanish but even for the Spanish-handicapped, there should be little trouble reading the tables.
Nicaragua offers lower elevations on the east and west coasts plus most of the southern part of the country. Mountains divide the east and west sides with little population in the mountainous area except within possibly 30km of the Pan American highway.
The lower elevations are the hottest as, in the tropics, temperature is pretty much just a function of altitude. Getting up above 800 meters gets you into climates that are still warm but never "too damn hot". (This page offers Nicaragua weather information as reported by Weather Undergound.
The Atlantic coast tends to be wetter than the pacific, more remote and less populated. Also, many parts belong to indigenous people who were granted autonomy.
If you are looking for "Gringos", you will find the highest concentrations in the Granada and San Juan del Sur (in the department of Rivas) areas. While I have yet to really find an area hostile to people just because they are non-locals, you will find Gringos few and far between in areas such as Chontales and areas north of Esteli.
For those people asking the question "where should I look around", there is no general answer. That is, if you want to be where the Gringos are, I just told you. If you like cooler temperatures, you should be looking in the mountains. If you want the beach--you have two long coasts to explore.
The best generic advice is that if you are seriously considering moving to Nicaragua, spend as much time here as you can first. When you arrive, bring as little as possible, rent a place to stay and continue your research. After a year you will likely be able to answer this question for yourself.