Death Note plays more of a dramatic, dark and strategic role, it has it's goods, but also can get very boring in parts. The plot itself is semi-predicable, but still enjoyable to watch. The art is actually pretty good, taking a very realistic aspect.
Code Geass has one of the best plot I have seen so far. The use of mecha weapons is actually a downer for me, as I dislike robot fights, but the fights are still enjoyable regardless. The art is good, but the skinny people may be a little disturbing to you in the beginning. Code Geass is actually a good ride to go through.
Now, for a much more personal reference, I would recommend watching Fullmetal Alchemist: Brotherhood if you haven't watched it yet. It easily comes on top of both DN and CG.
