Following one of the article from 2013 :
Before you start hammering that “add to shopping cart” button, note that the general impression around the web seems to be that the Leonardo still has a few bugs that need ironing out, and isn’t quite as beginner friendly as the Uno. For builders already familiar with Arduino, this is the better deal.
The question is if Leonardo is still buggy and may cause any confusion to newbie Arduino programmers. Furthermore, Leonardo doesn't have removable chip, so how can one transfer the project into a separate processor and use Arduino to the other project?