As I said before, Granada is a relatively safe and charming city filled with lots of colonial architecture and a real laid back feel to it. There is a large expat community there as well.
Compared to Leon, Granada is a much smaller town and has a high percentage of tourists and backpackers coming through there year round.
Leon,is the second largest city in Nicaragua and is a major university town which gives it a more vibrant and youthful feel than Granada.
There is lots of shopping and outdoor markets where you will find plenty of fresh fruits and vegetables daily and despite being a big town, it is compact enough where you can easily get around without a car. Leon has a lot more "local" feel to it and the night life is very vibrant here, especially on the weekends.
Housing can be much cheaper here in Leon and the tourism is slowly growing but just enough so you don't experience the higher cost of living you will see when you compare prices between the two cities.
Regardless of which city you choose, Nicaragua is on its' way to becoming the new "it" place to live and retire in Central America. You won't go wrong either way!