The primary antagonists of the Transformers franchise, The Decepticons are a faction of transforming mechanical beings who hail from the planet Cybertron and seek to bring the galaxy under their heel. The conquest is opposed by the heroic Autobots, another faction of Cybertronians who believe in freedom rather than tyranny; the Autobot-Decepticon war frequently brings itself to Earth across the annals of Transformers fiction.
The Decepticons are usually led by the awesomely powerful former gladiator Megatron, but being deceitful beings by nature, internal power struggles within the Decepticon ranks are a frequent event. Let's take a look at some high-ranking Decepticons, who have either led or fought to lead the faction at one point or another.
10 Better: Shockwave
Known for his cyclopean head and cannon-affixed left arm, Shockwave is one of the strongest and most intelligent of the Decepticons. A scientist at heart, Shockwave is ultimately loyal to his own agenda and sees the Decepticons as a means-to-an-end; that end being the betterment of Cybertronian-kind. A creature of logic, Shockwave is content to serve Megatron if the latter proves a successful leader, but if he doesn't, Shockwave has no compunctions about assuming command, which is exactly what Cybertronian cyclops did just that in the original The Transformers comics published by Marvel.
After the Decepticons' humiliating defeat in the 4th issue, Shockwave destroys the remaining Autobots and assumes command from Megatron. The remainder of the series' first half would see power struggles between Shockwave and Megatron, though the former tended to last longer as leader and be more successful when doing so. After all, it's only logical that Shockwave is the right leader for the Decepticons.
9 Worse: Starscream
Megatron's second-in-command, Starscream's defining trait is his desire to usurp Megatron. Unfortunately for him, that when he does briefly grab power, it invariably blows up in his own face and that of his fellow Decepticons.
A coward and egotist at heart, Starscream is ultimately too short-sighted and arrogant to be an effective leader, especially since he commands neither Megatron's raw power nor his charisma. Starscream's dreams of leading the Decepticons may be glorious to him, but for the other Decepticons, they might as well be bad comedy.
8 Better: Soundwave
The Decepticons' communications officer and spymaster, Soundwave possesses an exceedingly rare quality among the Decepticons: loyalty. Genuinely devoted to Megatron and his ideals, Soundwave is his leader's right-hand in all but name, and one of the few Decepticons that doesn't dream of leading the faction himself. Ironic, for if he were thrust into leadership, Soundwave could easily excel. Soundwave is both crafty and a skilled fighter, qualities needed in any prospective Decepticon leader, but he also possesses an even more powerful skill: telepathy.
Soundwave can decipher the electronic signals that make up a Transformer's thoughts, and while he's content to use his abilities to serve as Megatron's snitch, as leader he would be able to peer into both the minds of his Autobot adversaries and any traitorous Decepticons, keeping the troops in line through fear. Soundwave superior, indeed.
7 Worse: Thunderwing
Thunderwing is a Pretender, a unique type of Transformer who takes the "Robots In Disguise" idea to a new level; Pretenders wear armor that disguises them as an organic alien being. Of the Decepticon Pretenders, Thunderwing is the most powerful, and he's a skilled commander to boot; for a time in The Transformers Marvel run, Thunderwing led the Decepticons on Cybertron in place of the absent Megatron. He didn't last long, however, for one reason: obsession.
When Thunderwing fixates on something, particularly the Matrix of Leadership, he will stop at nothing until he possesses it, often falling into insanity in the process. Compare this to Megatron, who while certainly driven, manages to retain enough lucidity to balance his goals and his tactics.
6 Better: Onslaught
When the Decepticons' plans fail (as they frequently do), it's often because Megatron failed to think them through. As such, who better to replace the current Decepticon leader than a strategist? Onslaught is the leader of the Combaticons, a group of 5 Decepticons with military-themed vehicle modes who can combine into Bruticus, a towering figure of which Onslaught forms and torso.
Onslaught's strategies and skilled leadership means the Combaticons are among the most skilled and successful sub-groups of Decepticons; as shown in Fall Of Cybertron, when Starscream temporarily took command of the Decepticons, it was only Onslaught and the Combaticons who kept the Air Commander's reign from being a complete disaster. With a winning track record and the right head for leadership, maybe Onslaught should be in-line to receive a promotion.
5 WORSE: Ratbat
Despite his diminutive size and non-threatening alt-mode (a micro-cassette. Ah, the 80s), Ratbat led the Decepticons for a period in The Transformers Marvel comics. That he hasn't returned to the role should give you an idea of why elevating him to the position was a bad idea. A bureaucrat at heart, Ratbat sought to limit the Decepticons' energy consumption, often having a debilitating effect on the Decepticons' plans in the process.
His physical weakness also came back to bite him when Scorponok killed him with a physical shot in the back. When you're leading a group of alien war machines, maybe the leader should resist being able to be felled by a literal stab-in-the-back.
4 Better: Scorponok
Scorponok leads the Decepticon Headmasters, a group of Cybertronians "Binary-Bonded" to men from the planet Nebulos; true to their name, the Headmasters' heads can detach and transform into armored suits for the Nebulans, with Scorponok's partner being Lord Zarak. This innovation is emblematic of Scorponok's character; unlike Megatron, who generally seeks conquest and power for their own sakes, Scorponok wishes to see the Cybertronian race evolve along Darwinian lines.
Scorponok even once defeated Megatron and assumed command, in the Montrosity mini-series, when he felt his leader wasn't strong enough to lead the Decepticons. A struggle for leadership is survival of the fittest, and Scorponok is certainly among the fittest Decepticons there are.
3 Worse: Tarn
Leader of the Decepticon Justice Division, whose job is to execute any Decepticon traitors or deserters, Tarn is a true fanatic. He wears a faceplate modeled after the Decepticon insignia to mask scars he received in a fight with Grimlock, Tarn idolizes Megatron, having his entire manifesto "Towards Peace," memorized by Spark.
However, while awesomely powerful, he's still not quite as strong as his ideal, and this plus his fanaticism means he'd likely come off as a pale imitation of Megatron were he to assume command of the Decepticons as a whole. Plus, given his line-of-work, he's sure to have more than his share of enemies in the Decepticon ranks who would undermine his prospective leadership.
2 Better: Cyclonus
When Unicron remade a dying Megatron into Galvatron, he also created new troops for the reborn tyrant. The foremost of these was Cyclonus, forged from the corpse of fallen Seeker Skywarp, who became Galvatron's second-in-command. Cyclonus was soon forced to act as the Decepticons' de-facto leader both during Galvatron's disappearance and after it, for Galvatron had been rendered insane and borderline-incapable of commanding the Decepticons.
Loyal to his leader, Cyclonus kept the Decepticons in-line during Galvatron's bouts of insanity; in the process Cyclonus proved he could be a worthy leader himself if he ever wanted the position. He doesn't, however, and Galvatron should be thankful that, unlike his former self, he has a second-in-command so dedicated.
1 Worse: Scourge
Created from the deceased Thundercracker alongside Galvatron and Cyclonus, Scourge inherited his former self's uncertainty, but whereas Thundercracker's weariness was born of uncertainty in the Decepticons' goals and whether he belonged with them, Scourge is just plain whiny. Lacking the skill or resolve of Cyclonus and unable to keep his personal troops, the Sweeps, in-line without threats from Galvatron or Cyclonus, it's not hard to see why Scourge was passed over for Galvatron's second-in-command.
Scourge did briefly lead the Decepticons in The Burden Hardest To Bear after stumbling into possession of the Matrix of Leadership, but was soon defeated by Hot Rod, who reclaimed the Matrix and became Rodimus Prime again; a short tenure as leader that proves why Scourge shouldn't return to the position.