Some Transfomers are stronger than others, regardless of their transformations. Even the most unlikely alternate modes unfold to unleash some of the universe's toughest Robots in Disguise. This doesn't just include the Autobots and Decepticons, but also the deities seen in the Transformers Universe.
These Transformers boast immense physical power and incredible techniques, making them indispensable on the battlefield. Others combine the might of other Cybertronians into one unit, creating terrifying "gestalts." When power isn't enough, size more than makes up for it, with some of the strongest Transformers also being the biggest.
10 Grimlock
The leader of the Dinobots and a popular character ever since Generation 1, Grimlock is known for his tyrannosaurus alternate mode and fittingly fierce attitude. He's extremely tough in both forms and can even breathe fire in beast mode. What he generally lacks in intellect he more than makes up for in power.
In most continuities, Grimlock is easily one of the strongest main cast members. In fact, he's usually portrayed as being at least as strong as powerhouse Transformers like Optimus Prime, Jetfire, and Megatron. Unlike the former, he can also fly without any outside assistance, making him even more of an asset.
9 Devastator
The first Combiner/Gestalt in the series, Devastator is the combined form of the six Constructicons. Simple-minded in his pursuit of wanton violence, Devastator's only aim is to destroy whatever's in his path. Possessing an extra team member compared to most other Combiner groups, it's no wonder that Devastator is typically shown as being so hearty.
One of his greatest feats is surviving lava from a volcano. Additionally, he has proven able to fend off the enraged might of the Dinobots, and served as a rival for the Titan-class Autobot Omega Supreme. His main limitation is that he uses an early version of the Combiner technology. Despite this, he's still quite popular, even inspiring the title of the video game Transformers: Devastation.
8 Predaking
Predaking was another Combiner who was introduced after the events of Transformers: The Movie. Combining the animalistic ferocity of the G1 Predacons, Predaking was able to stand against both the Dinobots and the arrogant Sky Lynx. This made him easily the most popular of the later Combiners.
His later advancements made him stronger than the likes of Menasor and Bruticus. Additionally, he wasn't a complete brute like Abominus. Combining wild fury with incredible power, he was definitely a cut above the almost mindless warriors that other teams merged into. This eventually saw him return in a new form during the events of Transformers: Zone.
7 Fortress Maximus
The third major Titan-class Autobot in G1, Fortress Maximus's alternate mode was a gigantic battleship that combined with a smaller robot that formed his head in robot mode. He was a major part of the later G1 cartoon episodes and even the Marvel Comics G1 series, where he was binary bonded with the Autobots' human ally Spike Witwicky.
The version from the anime Transformers: The Headmasters was so mighty that he needed a "Master Sword" to become Fortress Maximus. Unfortunately, this was also a major limitation, since stopping him from drawing the sword prevented his transformation. Likewise, separation from the head unit had a similar result.
6 Scorponok
The original G1 version of Scorponok was the rival of Fortress Maximus, and seemingly just as powerful. He had many of the same resources, including smaller partners that fought alongisde him. Unlike Fort Max, Scorponok wasn't a "double Headmaster," giving him less of a weakness by needing only one head robot.
Likewise, Scorponok didn't have an equivalent to the Master Sword. While this left him without a comparable weapon beyond his gun, it also meant that his transformation wasn't tied to an external device. This made it much easier for him to transform and go on the attack against his enemies.
5 Metroplex
Metroplex is actually a segment of Autobot City, albeit a sentient part that can transform into a robot. Metroplex had less of a one-track mind compared to Omega Supreme. He was also simply a stronger and bigger Autobot, dwarfing the power of even the combiner teams.
Since he wasn't a Headmaster, Metroplex had a major advantage over Fortress Maximus. One big drawback of Metroplex, however, is that he needed a transformation cog to turn into his robot form. This led to an extended sequence in the beginning of the third season of Transformers in which Metroplex was completely helpless until Wheelie and Blurr supplied him with said cog.
4 Trypticon
Trypticon was the first Decepticon Titan-class figure, and he was a massive beast indeed. His main robot mode was a gigantic robotic dinosaur, and this form was matched with tons of physical power. Although he was far more dim-witted, this made Trypticon a worthy match for Metroplex.
Additionally, Trypticon doesn't require a transformation cog to transformation. This allowed him to go into robot mode much faster. Conversely, his status as a Decepticon meant that he could also fly, an ability that Metroplex lacked. Still, he wasn't very intelligent, which allowed others to easily outsmart him.
3 Piranhacon
The last major G1 Combiner in the West, Piranhacon was the combined form of the Seacons. According to the Marvel Transformers guidebooks, he had the most physical strength of any Combiner, far eclipsing even some of the city Transformers. On top of that, one of his combiner units turned into a gun, making him the only Targetmaster Combiner.
Sadly, the Seacons are some of the most obscure Transformers, meaning that their strength is rarely showcased. They have no clear Autobot rival, which again speaks to their power level. As a later combiner, this incredible strength can be explained as advancements in the Combiner technology.
2 Primus
A far cut above any of the more common Transformers is Primus, the god of their entire species. Like his children, Primus also has an alternate mode, with his being the planet Cybertron itself. He created the Cybertronian species through the body of his planet mode, using them to fight his evil brother.
Unfortunate, the constant warring on Cybertron weakened Primus, to the point where the planet became a lifeless husk. Thus, it's rare for Primus to ever assume his robot mode. Likewise, his constant dormant state is what initially caused the Autobots and Decepticons to seek out other sources of energon.
1 Unicron
The evil brother of Primus, Unicron is a devilish Transformer who consumes whole worlds in his own massive planet mode. Unlike his brother, Unicron was never dormant, and was freely able to transform into robot mode. He also had the ability to move throughout dimensions and planes of existence.
Just as Primus created Transformers from his own body, Unicron could reformat his heralds. He turned the dying Decepticon leader Megatron into Galvatron, doing the same for others in his ranks. He even inflicted great pain on them to control them, showing just how much power he wields over those who serve him. Weak only to the power of the Autobot Matrix of Leadership, Unicron is easily the most powerful of all the Transformers.