Let's look at it at Suzaku's POV as to why he considers Lelouch more evil than him.
1. Killed Euphie.
2. Ordered Euphie to cause a massacre.
3. Dragged Euphie's name to the dirt.
4. Used massacre to create a larger rebellion.
5. Lelouch was never remorseful in front of Suzaku.
6. Called Euphie as a thing of the past in front of him.
7. Large chance that Shirley was killed by Lelouch for regaining her memories.
Yes, even I would consider Lelouch more evil than Suzaku from where Suzaku's coming from.