Code Geass. I prefer it to Death Note because of how the story plays out. Death Note also just was a bit boring after L died and I didn't like how they acted afterwards. Mello and Near were okay and all but it just seems that Light wasn't all into besting them. He just wanted them dead so they didn't get in his way. Also,the animation,the plot and the main characters from Code Geass are better. There's a bit madami humor,less annoying characters and pangkalahatang better plot structures.
If I had to choose Death Note. I like how it proved a series doesn't need a bunch of action or blood for a series to be really exciting and keep you on the edge of your seat. I just loves the way Death Note bent my mind and really made me think. Though, I pag-ibig Code Geass as well~
Plot wise, I prefer Death Note because I just pag-ibig how mind bending it got at times. It was an pangkalahatang joy to watch for me and it still remains my paborito anime.
Character wise, I have to say I prefer Code Geass's. It's not that I dislike Death Note's characters, I really do pag-ibig most of them, it's just that the Code Geass set of characters were madami interesting to me.