Here is actually a good review of Nuffnang versus Advertlets, so if you want to have a comparison review between the two, just read that post. I am not sure whether it was totally a coincidence that both companies were launched several days apart from each other in the same month, but oh, well.
And in case you are wondering, I am sticking to Nuffnang at the moment as the official blog advertising network of Kerajaan MENJ (believe me, its a steadily growing empire). The ads in Advertlets may be AJAX-ified and all, but I really do not see anything in there apart from a poll. Maybe I’ll be inclined to put up Advertlets in one or two blogs once they start to roll out their advertising.