Both are crime dramas with a focus on psychology and motive. Aku no Hado gets the viewer inside the head of a serial killer while Strawberry Night Saga is from the perspective of a victim turned detective.
Serial killers galore. Bishoku Tantei Akechi Goro is more of a dark comedy with lots of violence and blood combined with a quirky sense of humor, whereas Aku no Hado is pretty much just nail-bitingly intense. I like both of them for what they add to the genre, but for different reasons.
Serial killers and more serial killers. Both dramas deal heavily with serial killers and the police attempting to catch them. The pacing is tighter in Aku no Hado, but Yuki Furukawa and Nattarat Nopparatayapon are equally proficient at playing super creepy dudes.