Nellson, I faced the same issue with one of my courses this semester, one that I do for another university that is using D2L. I used D2L around 5 years ago but have been using Moodle myself for 5 years, so in a way, I was eager to use D2L and see how it compares. In my own courses, I use Quizzes, Discussions, and Assignments, so part of an overall comparison might depend upon what other faculty tend to use. I am now done with my D2L course, and was very disappointed. I am one who likes to separate the two products by "What the student sees" and "What the instructor see."
From the student perspective, students might not see much of a difference. However, in D2L, students never see "online users", so getting a sense of knowing if other students are doing work or the instructor, this seems missing in D2L. Also, the grade book is not as powerful. I think my students like seeing their grade updated regularly, and this was not possible in D2L following my course's simple grading structure. Believe me, I tried my best with the school's D2L support team. Eventually, I ended up using Excel to do the calculations, and importing the status into a D2L grade item. I never have to do this with my Moodle, so I feel that student's knowledge of their status was limited with D2L. The Discussions on D2L take on a somewhat clumsy view, not nearly as nice as Moodle. Having noticed these differences, I must say that probably students do not because they know no difference. They accept these shortcomings because the never see that a system could be better.
From an instructor perspective, there are lots of differences. D2L's grade book, probably better than Blackboard's, still doesn't compare with Moodle's. Being able to read and rate discussions, in context, is a major strength of Moodle over D2l. And Moodle's quiz engine is much more powerful. I wanted to give online exams, for example, and really missed Moodle's "Calculated multiple choice" question type. My exams were much less randomized in D2L (but students would never complain about this, right?). Also, getting questions into D2L was a mess. When I probed with the school's D2L support staff about this quizzing inadequacy, they said that many faculty are now using the publisher's website for quizzing, not D2L. In checking about why other faculty are not bothered by what I was learning, I was told that I am a much more demanding instructor, and that most instructors only post lecture notes (PowerPoints) and post the final course grades. So they were really not using the other features of D2L.
So, here is what I am going to try next semester. Since it is okay to link to an external quiz engine, I am going to link to my Moodle's quiz engine. In my course, I don't use Forums that much, but when I do, I am going to link to a Moodle forum. Yes, students will need to log in (again), but they can set up their own username and password, so I don't see this a much trouble. I am also going to use the Moodle garbed, linking to it from D2L. I am basically going to mirror the course between the two products, using Moodle for the features that are better. For "content", I always link to webpages on my website, so it is rather simple to do this in any product. In this manner, I can still tell administrators that I am using D2L, and they should be happy. I find that most administrators don't really know what an LMS can do, so they just want the simple "I use D2L" being said. I did keep careful notes about D2L's problems, just in case I ever need to explain this to the administrators.
Since I will be running parallel systems, and students will be able to do everything in Moodle, I will be asking student's opinions about Moodle at the end of the semester. I the beginning of the semester, I am going to tell students that I am using this external "moodle" product for its better grade book, and for better managing their ability to practice quizzes, so that their learning can be maximized. Hope this gets them over the hump. The only "negative" issue might be that students need to do one extra login to Moodle.
Eventually, I plan to document all of the differences that I uncovered between the two products.
(BTW, D2L apparently does not support emoticon!)