Doctor Strange is the Sorcerer Supreme and one of the most powerful characters in the Marvel Universe as a result. Whenever someone needs help, they often find Stephen Strange, and when the world needs to be saved, he is invariable in the mix to save the day. However, he is also arrogant, often self-centered, and might not always be the best person to hold the role.
With Doctor Strange taking center stage in the Marvel Cinematic Universe and showing a possible penchant for rash decisions in the trailers for Spider-Man: No Way Home, there are always better choices for the role of Earth's greatest sorcerer in the comics. Whether looking for the next Sorcerer Supreme or finding someone who could replace Doctor Strange if need be, there are plenty of options in the Marvel Universe.
Doctor Voodoo
Doctor Voodoo is one of the most powerful sorcerers in the Marvel Universe and he even served as the Sorcerer Supreme when Doctor Strange was no longer in that role. He also taps into his powers from the Vodu gods and they gave him abilities that are above and beyond basic sorcerers.
He proved to be a fitting replacement and the Eye of Agamotto chose Voodoo specifically to replace Doctor Strange, proving his worth and value in the role. His best traits are his pure heart and his willingness to always fight for the greater good.
Agatha Harkness
This might seem strange for people who only know Agatha Harkness from the MCU and WandaVision, but the character in the comics is much more trustworthy and honorable. In the comics, she is a very old witch, her earliest memories from the era before Atlantis sunk below the seas.
She has trained several sorcerers on Earth and has taken a strong sense of attachment to Wanda Maximoff in the comics. Agatha Harkness has worked alongside heavy-hitters like the Fantastic Four and Silver Surfer and has proved time and time again that she is someone who can help fix almost any problem, and would make a perfect Sorcerer Supreme.
Doctor Doom
Doctor Doom might be the last person that someone would want to see hold the title of Sorcerer Supreme, but he is also someone who would hold the power and wield it masterfully in the right conditions.
At one point, Doom even turned good and worked as an Iron Man character for a time, and his combination of magic and science is unparalleled. It seems that every time that Doctor Strange is removed from the picture, Doom's name comes up as a possible replacement. He was actually the runner-up when Strange earned the role.
Scarlet Witch
Scarlet Witch has some problems when it comes to holding the power of the Sorcerer Supreme. This is mostly due to her habit of trying to do the wrong thing at the wrong time and always making things worse. Scarlet Witch creating House of M and bringing zombies to Krakoa are two examples of this.
However, since she returned to prominence, Wanda has met her mother on the mystical Witch's Road and learned how powerful she really is. Wanda has worked hard to make up for past mistakes and has been studying to become a more reliable and powerful witch, and she is on the road to proving to be a great candidate for the Sorcerer Supreme if need be.
Wiccan
If Scarlet Witch is a possibility for the Sorcerer Supreme based on her powers. there might be someone even more powerful to step into those shoes. Wanda's son Wiccan might have more magical powers than his mother if his alternate timeline future is any indication, and he has a lot more control over his emotions than his mother as well.
In at least one alternate timeline, Wiccan becomes the all-powerful Demiurge, the being who seeded the Earth originally and helped give birth to the Elder Gods. While that is a frightening fate, his reality-warping powers rival his mother and his pure goodness as a hero would make him a perfect Sorcerer Supreme if offered the chance, and Doctor Strange even said he was a candidate.
Wong
Wong is not the same in the comics as he is in the MCU, although there is a chance that could change in the future, especially with the popularity of Doctor Strange's close ally in the movie and TV world. In the comics, Wong was Doctor Strange's butler and his only power was his martial arts skills.
In the MCU, Wong has magical powers that rival Doctor Strange, although he remains a step below the Sorcerer Supreme. However, one thing that the MCU has shown is that Wong might be more fit for the role than Strange due to his careful choices and wise decisions. Move the MCU's Wong to the comics, and Strange would have direct competition for the role.
Loki
Loki actually became the Sorcerer Supreme at one point, taking the title right from Doctor Strange. This happened when a mystical game took place where Vishanti wanted to determine the true Sorcerer Supreme and in this recent game, Vishanti wanted Loki to be the new holder of the title rather than a mere mortal.
Doctor Strange eventually took the title back, but Loki held it and was powerful in the role. In the comics, Loki is now a hero, giving up his role as a villain and moving into a better place in his life. If he received the role now, he would surely be a more virtuous Sorcerer Supreme than the last time and is a worthy successor.
Magik
Magik is a Sorcerer Supreme at this time, but is she as good as Doctor Strange? Stephen has gone to Illyana for help more than once and she has proven over time she is worthy of the role she holds. The mutant is the powerful Sorceress Supreme of Limbo, the dimension she rules over.
Illyana served as the pupil to Doctor Strange in the main reality, learning from him how to control her powers. This gave her the ability to earn the position in Limbo. There was also a storyline titled Doctor Strange: The End where he sacrificed himself to bring magic back to the world and named Illyana his successor.
Nico Minoru
Nico Minoru is a member of the Runaways, the team of teenage heroes who ran away from home when they learned their parents were supervillains and then learned they shared superpowers as well. There are some immensely powerful heroes in this group of kids, and Nico Minoru might be the most powerful.
There is also the chance she might be one of the most powerful heroes in the entire Marvel Universe. She knows right from wrong and will always do the right thing and has access to dark magic as well thanks to her lineage. The only thing holding her down was her lack of training, but that could easily be fixed with the right mentor.
Strange Academy
Doctor Strange knows that he won't be around forever and knows that the world needs a new Sorcerer Supreme when he is gone. That is why he started his own school in the Strange Academy. While there are plenty of options already in the Marvel Universe, including Doctor Voodoo, who is a teacher at the school, Stephen wants to pick his own successor.
The kids in this school are all interesting possibilities. Doyle Dormammu is the demon Dormammu's son. Dessy is the daughter of the demon S'ym. Emily Bright is a human-born sorcerer and a very powerful one at that - without demonic parents. There are plenty of options in the school, but as kids, they have a long way to go to replace Doctor Strange as the Sorcerer Supreme.