The usual rule for many TV shows is that the main character tends to be the most likable one. However, that's not always the case. Sometimes the leading character can be somewhat despicable or there are simply many more heroes who also become fan-favorites. The Flash falls into the second category.
Naturally, the show focuses primarily on the titular speedster. But even though Barry Allen is the show's main character, the series wouldn't be the same without a large number of other characters, both heroes and villains. Some of them are then more likable than others, just like people tend to be in real life as well.
Eobard Thawne
Eobard Thawne is one of Barry's most relentless villains. He kept appearing on the show even after his supposed death in season one. There's no denying that Thawne is highly intelligent and cunning. But the awful deeds he has committed make him less than sympathetic.
He killed Barry's mom, murdered the original Harrison Wells, stole his life, and manipulated Barry's and Iris's daughter, Nora.
Harrison Wells
A lot of the Harrison Wellses aren't as sympathetic as the other heroes. That is possibly because they can come across as overly cold, strict, distant, or unemotional.
Some of them were even close to arrogant, such as Sherloque Wells. Harrison Wellses bring their intelligence to the team, but with the exception of H.R., they aren't that warm or likable.
Allegra Garcia
It's more than possible that Allegra will eventually rank higher since she hasn't had the opportunity to shine just yet. Allegra's a good person who wants to help the team the best she can.
But she has the tendency to beat herself up over things that aren't her fault which might annoy some people. She was also unnecessarily strict with Nash after she learned the truth about his past.
Ralph Dibny
It's unclear what part, if any, Ralph will play in the current and upcoming seasons. But before, he was a valued member of the Team Flash. Ralph wasn't always sympathetic, as before he joined the team he was more of a criminal who could be rude and sleazy.
He turned things around when he became a superhero and was supportive of others, especially Caitlin who struggled with being a Killer Frost. Ralph's clueless nature sometimes drove the fans nuts but overall, he's a good guy.
Iris West-Allen
Iris is by no means a bad character. However, some fans of the show don't like her. One of the reasons might be that she hasn't had that many solo storylines as she would have deserved. Not having proper shine can make for someone who isn't as developed as they should be.
Iris can also come across as overly strict and not so understanding when it comes to the emotions and situations of other people. With that said, there's no denying Iris means well, as she has a good heart and wants to be there for her family and friends.
Caitlin Snow
Caitlin is one of the characters who suffered the most throughout the course of the show. She lost Ronnie twice, her boyfriend turned out to be a psychopathic speedster, her dad died, and Caitlin also had to deal with the fact she had ice powers and turned into Killer Frost.
Despite that, she maintained her good nature. Caitlin is always there for her friends when they need her, and she still manages to smile and make people laugh, which is a small miracle considering her past.
Cisco Ramon
Cisco Ramon is a vital member of the Team Flash. He's also one of Barry's closest friends. His intelligence and desire to help make him someone others can rely on.
The only fault Cisco has is that he sometimes falls into despair, and it might take him a while to pull himself out of it. However, that's something people can relate to and sympathize with, especially since Cisco's life hasn't been all that easy.
Cecile Horton
It's no wonder that Cecile and Joe got together - they're very evenly matched when it comes to their warm personalities. Cecile has a strong instinct to help and protect people, just as Joe does. Her mostly optimistic nature and kindness made her one of the fan-favorites shortly after her first appearance on the show.
Plus, she has a sense of humor and sometimes freaks out in dangerous situations which makes her even more relatable to the audience.
Joe West
It's hard to dislike Joe West since character-wise, he's one of the best people on the show. Not everybody would take in a child whose mother has been murdered and dad ended up in prison, but Joe did this.
He's a great father to his kids, is always there when they need him, and has a kind word or advice for them at every turn. He also works hard to protect the city from criminals and evil metahumans even though Joe himself has no special powers.
Barry Allen
Barry is by far the most sympathetic and likable character on the show. It's possibly because he is the focal point and it's easy for the fans to understand where he's coming from. Barry has some faults, like everyone, and makes errors in judgment from time to time.
But he more than makes up for this with his desire to do good, and with his usually optimistic nature. Barry wears his heart on his sleeve so it's almost impossible to stay mad at him for long.