Sigh, I wrote a whole long post explaining why I thought they were both about the same, in my opinion, and then I accidently closed the page...sigh.
I'm not rewriting the whole thing again, so I'll just paraphrase myself:
I think they're both great in their own sense, and I believe Death Note has a deeper intellectual battle, while code Geass has a good intellectual battle, with awesome powers and mechas. Overall, they both have the depth and epicness of each other, just in different ways.
So my opinion is neither is better than the other, and both are epic.
Now if you asked me which ending I liked better, I would say, 100%, Code Geass' ending was so much better, and more epic. I loved the way it ended, and so, in my opinion, Code Geass has a far better ending.