The most powerful character I ever created was pretty blatant, and it was actually the character that I made for my first ever forum roleplay. Well, he wasn't created overpowered, but he got there through shenanigans. It was a free for all roleplay in the Spam section of a non-roleplaying forum that used to be my primary place of internet activity. By 'free for all' I mean that there wasn't any real oversight by the GMs to keep characters in check, so combat became power level contests full of last second power up gambits very frequently, but that was fine because we all sort of balanced out by all becoming brokenly overpowered.
My guy started off with a sword that could disintegrate anything it cut and some generic superhuman strength/speed/endurance stuff, and he wasn't anywhere close to the strongest character in play at that point. However, through some collaborative ideas made with the co-GM who was in control of the big bad, he rather quickly became one of the most dominating forces in the game. He went off on a journey to the middle of nowhere because he felt something calling to him, and it ended up being some artifact thing that imbued him with power from the evil god (one of a pair of opposed good and evil gods) that made him basically a minor deity in his own right. The powers that this gave him was some literal omnipotence, meaning complete and utter control over every possible thing, in a small area around him, plus some hype mental things like godlike perception in a larger area around himself plus superhuman intellect and speed of thought to be able to actually comprehend his new power. As you might imagine, "I know literally everything that happens in this large area around my character" plus "I can think fast enough to damn near anything" plus "I can literally control everything that exists in this small range around my character" equals overpowered as fuck. He went from being a grunt in the evil army to being the big bad's strongest soldier. Despite this ridiculousness, the big bad was still defeated in the end thanks to the also god-powered good guy GM's character, but in the last moment the bad god dude threw extra power at my character for future shenanigans.
Shortly thereafter we did a sequel roleplay in which my character from the first one appear to be not involved, because he fucked off to the middle of nowhere to contemplate the loss of his patron deity (and to come to grips with the even greater power that others didn't know about, basically a vastly extended range of the god power zone plus near omniscience in a range best measured in thousands of miles rather than the couple miles of before). In that one I played a guy who was a cult of personality priest/prophet dude, who was preaching that the so-called heroes who had stopped the evil god from before were now ruining everything and needed to be deposed from their governance of the city. The prophet guy kept saying stuff about how the will of the gods would smite the city if the heroes weren't removed or destroyed, and he got a lot of the people of the city under his sway. After a while shenanigans mode ensued and the prophet said the wrath of god was on its way and then a few posts later my old character showed up, ready to fuck shit up hard and get the real party started; it turned out that priest guy was actually a sort of clone thing my character made of himself (he'd always worn heavy ass armor, so nobody had known what he looked like) and sent to prepare the way for a big ole gambit that would bring the evil god back from the purgatory type place he'd been sent. It worked, and more crazy fighting ensued, and my guy was only "stopped" in the end by the good side of the pair of gods showing up and throwing a bunch of power at him to balance out the evil.. also effectively doubling his range of power in the process, but that made him turn to actually helping to throw both of the gods into purgatory land where they would be in eternal conflict with each other and not fuck up the world any more.
So my character started off as a guy with a magical sword and some generic powers, but he ended up being basically a deity. Shenanigans he pulled over those roleplays included hastening a siege by riding along the stone wall and cutting a line in it with his magic sword to cause the big stone blocks to disintegrate, winning fights by just nicking people with his sword (though one guy ripped off his own arm to stop the disintegration effect from taking him entirely, which was pretty sweet), committing a seppuku style move to disintegrate himself but through god-powered shenanigans maintaining a consciousness that willed his individual atoms to fly off to somewhere else and then fucking combine back together and be totally fine after that, and as a matter of course doing that neat thing where a character calmly walks through a raging battle and absolutely nothing can touch him (because anything other than the ground/street beneath his feet that got within 10 feet of him would just disintegrate because fuck yeah god powers). It was hilariously broken.
Despite having played and enjoyed that character, I actually prefer more balanced levels of power. That one only worked and made sense because the whole roleplay was basically a game of people pulling powers and upgrades out of their ass to survive or get things done. Fights were less a matter of "who is stronger" than "who can come up with the most creative ways to get around the other character's powers." Despite my character being what would be brokenly overpowered in almost any other roleplay, he only ever killed characters that the player agreed should die and he took a fair amount of wounds even after reaching demigod status because people were able to come up with ways to get around his powers.
For the most part though, I prefer having characters who ride the average level of power. It's more fun when I have to actually struggle to accomplish things, just like any other player, rather than just breezing through obstacles with "lol check my power level scrubs, gg." Being weaker than the average can also be fun, but I usually prefer to do that by giving my characters various indirect handicaps and limitations on their abilities rather than straight up giving them less or weaker abilities than other characters have. For example, I've got a vampire illusion mage character (Zin from Legend of Renalta) who is naturally gifted with the illusion magic and has cool vampire powers that can make them even more effective, and together that could make her scary strong.. but she's a pacifist who's terrified of death so she is only just now coming to grips with how to make use of her abilities in combat in a non-lethal manner after having already gone through two dangerous missions. It's more fun for me that way, so that's how I roll.