As a graduate student in Humanities, I have been using the big Oxford-Duden as a main reference in my research. The big O-D is fantastic for this purpose, but it is way too big to carry around. So I had been looking for a smaller dictionary which fits into my backpack. I own Langenscheidt's universal dictionary to carry arround in my pocket when I'm in Germany, but that one's too brief to use in a more serious setting e.g., studying German at a language school. L's pocket dictionary (which is actually too big to fit in your pocket) is also a little too small. I have thus seriously considered the pocket O-D and L's compact dictionary, and L's is clearly the winner. Here are my reasons:
1. L's has pronunciation keys for german entries, while the O-D doesn't. (The O-D instead has pronunciation keys for English entries.)
2. L's has much more (30,000) words and phrases.
3. L's is much smaller. (They are both very thick. But while L's is a size of a small airport paperback, the O-D is much larger - it's about the size of a penguin classics, only much thicker. The O-D simply wastes much space - its pages have more space than L's, and its font is bigger. L's uses very thin dictionary papers, while the O-D doesn't.)
4. L's has much more idiomatic expressions (There are 15 of them for 'helfen' in L's and 2 in the O-D.).
My only problem with L's is that it does not have entry words in blue, as the big O-D and the pocket L's do. (The pocket O-D doesn't either.)