The cast of Star Trek: Lower Decks is a super lovable crew, they all have their own idiosyncrasies that make them fun to watch, but they're all pretty intelligent when it comes down to it. It's tough to make it in Starfleet, but, of course, but this crew goes above and beyond.
Some are certainly smarter than others, though. While Tendi and Rutherford are incredibly smart when it comes to science, they might not be as smart in other areas. The same goes for the rest of the crew. Either way, some characters are certainly smarter than others.
Boimler
Boimler might be smart in a few areas, but he's also severely lacking in just as many, which puts him at the bottom of this list. As an example, he's smart when it comes to going by the book, but the second that he's put in a position where he must deviate, he can't do it.
He also isn't exactly the best when it comes to people, which is necessary if one wants to ascend the ranks in Starfleet. He's smart enough, but he takes the lowest spot on this list for a reason. He's not all that much lower than the next entry on the list, though.
Ransom
Not all that much is known about Ransom, especially when it comes to the parts of his career that weren't shown in season one of Lower Decks. However, it stands to reason that he must be doing something right if he was able to ascend the ranks to Commander, not just anyone can do that.
Ransom also clearly has quite a solid knowledge when it comes to leading missions and keeping his crew safe. He might seem like a bit of a dumb jock at times, but it is pretty clear that he knows what he's doing, and that Captain Freeman is very much so satisfied with his performance in the role thus far. Unfortunately, viewers just haven't seen enough of him to assess how truly smart he is. Perhaps he's more intelligent than we know.
Mariner
Mariner is the exact opposite of Boimler, she doesn't play by the rules and has a huge amount of people skills. Her people skills are so good, in fact, that she's able to manipulate people to her desires whenever she needs to, which certainly comes in handy more often than not. In addition to this, Mariner is also very gifted when it comes to playing by her own book.
In situations when the rules might not be sufficient, she is able to very quickly come up with plans and ideas to keep herself and her allies safe, which is a hugely important skill to have as a member of Starfleet. When it comes to thinking on her feet, Mariner is at the top of the class. She's still not quite number one on the list, however.
Tendi
Tendi is incredibly intelligent in quite a few ways, and she displays this handily throughout Lower Decks. As a medic, she was essential to keeping the rest of the crew of the USS Cerritos safe while the Rage Virus infected people left and right. However, beyond being a talented medic, she also created The Dog, an AI dog that had enhanced abilities such as shapeshifting. And that was just a side project.
Beyond that, she's also incredibly skilled in combat, which she displayed when she accidentally found herself on a covert ops mission. Tendi's an asset in just about any situation that she finds herself in.
Freeman
Freeman certainly might not be the best Captain to ever grace the eyes of Star Trek fans, but she certainly isn't the worst, and it's undeniable that in order to become a Captain, one has to be a very talented individual who knows what they're doing.
While the USS Cerritos might not be the most important ship in all of Starfleet, it is nevertheless still a valuable asset. Freeman has shown off that she's a capable leader a few times, such as when she worked with her daughter Mariner to save the USS Cerritos and the crew of the USS Merced during a tractor beam incident. That could have resulted in many lost lives.
Rutherford
Rutherford is without a doubt the smartest member of the main cast on Lower Decks, and it really isn't even a close competition. While he might have the advantage of being the only character with a cybernetic implant, it certainly helps, as he is incredibly proficient at literally every job that he sets his mind on.
Whether it has to do with science or even straight-up fighting, Rutherford is going to get it done with ease. He also knows the Cerritos inside and out, and could basically run the entire engineering side of the ship by himself if he needed to. He manages to keep it together through some pretty tough events, despite it being one of the worst ships in Starfleet. That's power right there.