At this point in the Attack on Titan anime series, many different Titan types are known, but one is clearly more powerful than all the others. Attack on Titan season 4, part 1, which began airing in December of 2020 and wrapped up in March 2021, continued to develop some of the mind-blowing revelations from season 3, as well as offering even more insight into how Titans operate. With Attack on Titan season 4, part 2 set to release on January 9, 2022, the series is sure to determine once and for all which Titan reigns supreme.
For much of Attack on Titan's earlier seasons, Titans remain a total mystery to humanity residing within the walls. While the Scout Regiment does its best to conduct research and reconnaissance, they remain hopelessly unaware of how Titans work, and particularly how they are connected to regular humans. However, as the series has gone on, Attack on Titan's Titan shifters have gradually been revealed in more detail, to the point that now, both the Scouts and viewers have a solid working knowledge of which Titans exist and what their special abilities are: the Cart, Jaw, Armored, Colossal, Female, Beast, Attack, War Hammer, and Founding Titans, as well as regular/Pure Titans and Abnormals.
While each of these Titan varieties poses its own sort of threat, there is one Titan that clearly holds more power than all the rest. Unsurprisingly, this is the Founding Titan, which was kept hidden within the walls by the Reiss family for 100 years, and which is now wielded by Eren Jaeger along with his father's Attack Titan and the War Hammer, which Eren steals from the Tybur family towards the beginning of Attack on Titan season 4. Because of the Founding Titan's incredible strength and unique abilities, it's clearly the most powerful Titan of all.
Each of Attack on Titan's eleven Titan types is uniquely dangerous. Abnormals are completely unpredictable, while Pure Titans have essentially no human mind to reason with and are simply killing machines. The nine Titans are more powerful still, as they possess distinct traits useful for battle and strategic moves, such as the Colossal Titan's ability to evaporate everything within a huge blast radius or the Jaw Titan's teeth that are strong enough even to break Titan-hardened skin. However, the Founding Titan will always come out on top due to its status as the first Titan and the progenitor of all the rest. As such, it has the power to control other Titans and the minds of all subjects of Ymir (Eldians) whether they are Titans or not. Compared to the full range of this power, no other Titan, even of the nine, really comes anywhere close.
However, Eren's Founding Titan power hinges on Zeke because his half-brother is of royal blood. Eren may possess the Founding Titan, but its full ability to control Titans and Eldian minds can only be tapped into by a direct descendent of Ymir through the royal bloodline. Dina Fritz, Zeke's mother, passed this ability on to him, but Eren is the child of Grisha and Carla, and so lacks any royal blood. Thus, while the Founding Titan is undoubtedly Attack on Titan's most powerful Titan, Eren himself is not a perfect vessel for this power without Zeke because of his inability to access it on his own.