I did mine over about a year and a half.
If you are doing it over more than a few months, then try to start as early in the spring as possible, otherwise you'll get caught in the winter weather far too quickly.
I agree that doing it over a short period would mean that you retain more from each lesson. However, it would not be of much use if you learned to fly over 3 or 4 weeks, and then stopped for a few months as you had no money left.
You need to be able to keep flying after you get your licence, or you will forget what you have learned too quickly.