In my opinion, The Plutonian is the most complex, but Griffith is definitely the most well written here, if that makes sense.

Light is not complex ngl.

He's the most straight foward "Delusional God Wannabe" villain you can get. Legit the very first thing he did at the beginning of Death Note is immediately becoming a not-so-well intentioned megalomaniac with a god complex. No character development, no slow transition from "Anti-Hero to full blown Complete Monster" or anything. He immediately became a egotistical supervillain and that's that.