Light Yagami is one of the most insidious killers in anime history, originating from the Death Note story. He is able to kill targets after he has received their face and name, making it virtually impossible to detect him even by the talented L Lawliet.
However, he isn't the only Kira that posed a grave threat. Yoshikage Kira was a serial murderer who used his Stand, Deadly Queen, to incinerate his victims and leave virtually no evidence behind for his pursuers. By analyzing different qualities from each man, we can determine which of them is more lethal and terrifying.
10 Light - The Notebook
One thing which gives Light a significant advantage over Yoshikage is that he can indulge his killings from the safety of his own home. Conversely, his Stand using rival must physically be in the presence of those he murders, which would ultimately result in his exposure and defeat (as Hayato uncovered his identity).
Nonetheless, his notebook is not full proof. Once L became suspicious of Light, it was virtually impossible for him to use it, forcing him to delegate to others so that his killings could continue.
9 Yoshikage - Minions
Though Light's servants were invaluable in his work, few of them understood what he was doing, and they were often caught and killed so that he could cover his own tracks. Yagami's underlings were closer to roadblocks than threats in of themselves.
Conversely, Yoshihiro created dozens of Stand Users willing to protect his son, some of which had more horrifying abilities than Kira himself. An example includes Terunosuke Miyamoto, who was capable of paralyzing his opponents and turning them into laminated paper once they expressed a sign of fear twice.
8 Light - Intelligence
Light is much more intelligent than Yoshikage. Yagami was not only able to avoid being sniffed out through an extremely narrow list of candidates (granted, they were collected based on prior mistakes he made), he even joined the task force to look for himself.
Conversely, Kira went directly to the seamstress after he lost his button in his battle with Shigechi. More egregiously yet, even after his pursuers arrived, he would stay behind the retrieve it rather than immediately fleeing the scene. This would cost him his identity and nearly his life, proving an even greater blunder than Light falling for L's first trick.
7 Yoshikage - Identity Swapping
Yoshikage Kira may have been completely exposed during the middle of his arc (unlike Light, who concealed his identity until the end), but he was able to completely throw off his opponents' trail. This was accomplished through coercing Cinderella's Stand user, Aya Tsuji, to change out his face.
Once he had his new visage, Kira became impossible to track. The only reason Josuke and Jotaro Kujo were able to detect him later was because there was an informant against him in his own home. Otherwise, he would have been safe, and Shigechi would have died for nothing.
6 Light - Killing The Competition
Though Light would not be able to escape justice forever, he was able to outwit his greatest opponent, L Lawliet, through forcing a shinigami to write his name in her notebook. This was a stroke of genius, since she did not like him (only tolerating his presence for Misa's sake), and the detective was on the cusp of proving Yagami's guilt definitively.
Ironically, the only worthy combatant Yoshikage would permanently slay was Shigechi ~ a child who was not even actively pursuing him to begin with. However, were it not for Shining Diamond's healing abilities, he would have also been able to claim the life of Okuyasu.
5 Yoshikage - Bites The Dust
In the throes of greatest despair, Yoshikage developed a new Stand ability called "Bites the Dust." Essentially, should his identity have been revealed to anyone who was not a Stand user, those who were told would have their heads exploded immediately, and the day would be reset with their deaths cemented in fate.
This entails that should Kira have existed in Yagami's world, he would have been impossible to expose, as no one (including L) could have spoken of his identity once they have finally discovered it.
4 Light - Motivation
When analyzing the efficiency of a serial killer, one must examine the strength of their motives since it is correlated with their resolve. When he set about his mission, Light's goals were only to create a world cleansed of serial killers, chronic cheaters, and other such undesirables ~ technically, a selfless ambition.
Yoshikage's motivations are much more basic. All he wants is the severed hands of women to accommodate a fetish he developed in his youth. This makes him particularly shallow, visceral, and predictable ~ which Josuke would use to his advantage.
3 Yoshikage - Erasing Evidence
One of Kira's most useful features is the way he kills. His "Deadly Queen" does not only have a high destructive capacity, it can also concentrate the potency of its explosions to the extent where it does not even make a sound.
An example comes from when he followed a rude couple home from a train station. After murdering her boyfriend, he approached a woman and insisted to see her hand. Once he had finished complimenting it, we discover that it was the only part of her that was left from his Queen's ability.
2 Light - Deception
Lacking physical firepower of his own, Light's skills are stronger in deception than anything else. He was able to manipulate not only large swathes of emphatic followers but also the same few people still courageous enough to uncover his identity.
Yoshikage has attempted to deceive people as well (such as after his fight with Jotaro and Koichi, where he begged Josuke for help), but this has never worked to his advantage. He could only successfully fool Shinobu Kawajiri into thinking he was her husband, though unfortunately for him, her son was not as convinced.
1 Yoshikage - Death
Yoshikage's final moments were of utmost horror to those around him. He attempted to use his "Bites the Dust" ability on the nurse who was looking after him, and if successful, he would have erased the entirety of Josuke's efforts in subduing him. Only the excellent teamwork of Jotaro and Koichi was enough to staunch his Stand.
Conversely, Light's final moments were spent as a gibbering, incoherent mess, limping down a sidewalk as he vainly attempted to escape his retribution. Ultimately, he died without the Notebook and unthreatening to anyone.