Tsugumi Ohba and Takeshi Obata's supernatural crime thriller Death Note is an anime featuring two of the smartest men in all of anime and manga: the brilliant, but cruel Light Yagami (Kira), and the quirky, but genius detective L. They both swear to to see the other dead and prove whose brand of justice is right, and this dominates the first arc of Death Note.
Light wins this battle of wits, but that doesn't mean that L was a fool. Light had the advantage of the supernatural Death Note and Misa's Shinigami eyes, which allowed him to triumph. But aside from that, which of them is truly smarter? There are a few reasons to argue for each one.
10 Light: Uses His Home Field Advantage
This is actually pretty literal, as Light often uses his own bedroom as Kira HQ during his battle against L. L narrows down Kira's location to Japan's Kanto region, but no further than that, and Light's household is a pretty innocuous place. Light needs to protect the Death Note, and he takes extraordinary measures for that mission. With various traps in the bedroom door, he can determine whether someone has been there, and can even whether those intruders are police officers. Light also hides the notebook in a drawer's false bottom, uses a decoy book, and even rigs a fire trap in case anyone forces out the Death Note. L never got close to penetrating those defenses.
9 L: Hires Experts
While Light sees fit to use and discard people, L makes better use of his assets. This detective lives alone, but doesn't operate solo. He has dirt on both Aiber and Wedy, and makes repeated and excellent use of their skills and cunning. Aiber is a genius con man who infiltrates Yotsuba Corps as "Eraldo Coil," and Wedy is like Catwoman, being able to plant trackers and bugs all over Higuchi's property. She's also cool under fire and can restore shredded documents. L knows exactly how to staff his team!
8 Light: Uses Proxies
In both part 1 and part 2 of Death Note, Light is a slippery opponent, since he knows how to make use of proxies. He uses people constantly, but some are seen as more worthy of Kira's powers than others.
Light uses Misa as a second Kira for a time, and five years later in part 2, he uses the fanatical Teru Mikami as a proxy Kira, to great effect. He even uses Kiyomi Takada as Teru's own proxy, and Near and the other investigators soon get frazzled trying to keep up.
7 L: Has An HQ
Unlike Light, who has to use homegrown solutions in the battle of wits, L has a deep pool of resources (and knows exactly how to use it). Being a genius detective rather than a secretive serial killer, he can make use of police forces around the world and can even get his own skyscraper built in a matter of months. With this dedicated HQ, L can easily monitor Light and Misa (in case they're still Kira somehow), enforce ultra-tight security, and track down the new Kira with ease. It's quite an improvement over a mere bedroom!
6 Light: Doesn't Hesitate To Exploit People
While it's true that L has access to skilled pros like Aiber, Wedy, and Watari, he can't easily exploit someone he meets and get the most out of them. That would go against his moral code. But Light makes a deal with the devil to acquire the Death Note, and Light can easily use and later kill just about anyone, from Raye Penber to Kal Snydar to Kiyomi Takada and beyond. Light crosses boundaries that no one else would, and that makes him a wicked mastermind. He gets access to power anyone else would be afraid to touch.
5 L: Doesn't Get Cocky
While Light gets wrapped up in egomania and makes a few careless mistakes, L will never let anything slip. This famous detective survives this long against Kira because he will second-guess just about anything, and he'll take any cautious measure to be 100% sure of something. Even when Light and Misa "prove" their innocence in confinement, L won't let them go until he orders Soichiro to stage a murder attempt on them to see if they'll defend themselves as Kira. L isn't afraid to revisit an old suspicion if it gets him results.
4 Light: Fantastic Actor
Light Yagami is clearly a sociopath, and he can pretend to feel just about any emotion or feign any sort of personality if it pays off. He fools Naomi Misora into thinking he's a kind and warm fellow who wants to get her help with the Kira investigation, and he's stone-cold in the face of his father as Kira.
Soichiro desperately wants Kira arrested, and his very own son, Kira, never gives a thing away to a seasoned, professional detective like Soichiro.
3 L: Takes Bold Risks At Times
For the most part, L is cautious and careful like Light is, but at some point, he's ready to make a leap. Growing frustrated at the lack of solid evidence against Light, L envisions the perfect scenario: Light admits to L's face that he is Kira. L then enrolls at Light's university and confronts him, protecting himself and pressuring Light at the same time! Light is rattled by this move, and struggles to find a way around it for quite some time. So close, and yet so far!
2 Light: Cautious With A Cool Head
Earlier, it was mentioned that Light sometimes gets cocky and careless. He does this when his egomania as Kira gets in the way, to be sure, but otherwise he's a cautious one. Light is under constant pressure, and he admits very few openings of any kind for L, the police, Raye Penber, or anyone else to exploit. And when the flamboyant Misa joins Light's side, he's quickly able to get her up to his standards as Kira and keeps her safe for some time. L caught her eventually, but Misa would have gotten arrested far sooner if Light weren't so careful with her.
1 L: Knows Light's Personality
This is one of L's earliest deductions about Kira, aside from Kira's location in the Kanto region. L is soon able to figure out Kira's mentality: a young adult with an ego and a competitive side that hates to lose. L knows this because he is much the same way, and L exploits Light's personality in their battle of wits several times. More than once, this Kira-baiting nearly won the battle in L's favor, as Light will take nearly any bait that's offered.