Writing letters in LaTeX is very easy and fast after creating your own template. That's because you have only to change the address of the recipient, and the text. In other words: You won't have to modify the layout. Of course, you can do the same in MS/Libre Office as well. But then it is still not typeset. And: you won't have foldmarks and benefits of window envelopes. ;-)
A Template for Letters in LaTeX
The most advanced LaTeX class for letters is part of Koma-Script and is called scrlttr2. In the following you can download my letter template, which is based on scrlttr2.tex v0.3. by Juergen Fenn, as LaTeX code and pdf file. It shall be self-explaining.