To make things easy, consider hotels in the 5th or 6th arrondissements (districts), particularly the area known as the Latin Quarter. Near well known land marks, these are lively areas that appeal to most tourists.
You will not be able to visit all 20 arrondissements in only 3-4 days but staying in a central location will give you flexibility to easily reach the areas of greatest interest to you. There are numerous books that you might find interesting, including the Michelin Green Guide for Paris as well as various travel sites with information specific to Paris:
http://tinyurl.com/d3p85
http://tinyurl.com/mohlsvb