Starting at the very beginning of the Power Rangers franchise when Zordon first put the team together, the Blue Ranger of the team often serves a supporting role for the group. They aren't always the strongest member of the team, but they are extremely loyal, and more often than not, tend to have some sort of expertise that really helps the team.
The strongest of the Blue Rangers tend to be those that take charge, those that had Power Rangers skills before they donned their helmets, and those that continued to fight the good fight after losing their power. The weakest of Blue Rangers are those who just don't seem to click with the rest of the team, or just don't have the power to stand up with them.
10 Strongest: Chad (Lightspeed Rescue)
Power Rangers: Lightspeed Rescue breaks the mold of the first few seasons of the franchise. The Power Rangers are no longer teenagers, but adults who save the world as part of their job. The team might have some of the worst uniforms in the franchise, but they have some of the strongest Rangers.
Chad is recruited for the team in part because of his skills in the water, which is fitting since their base is actually underwater as well. Through most of the series, he seems like he's just a solid supporting player, but Chad proves himself quite a bit in the series. He regularly takes on bad guys on his own, and even teams up with a mermaid to help save the day at one point.
9 Weakest: Cestro (Mighty Morphin)
At the end of the Mighty Morphin Power Rangers run, the team needs a little help from Rangers from another planet. The Mighty Morphin Alien Rangers are from Aquitar, and their powers are very dependent on staying hydrated.
When the Rangers battle on behalf of the original team, they don't last long in a fight because they need water in order to power back up. Cestro is almost always the first of the team to find himself too dehydrated to keep fighting, making him the weak link in the team.
8 Strongest: Kevin (Samurai)
Kevin is the kind of Power Ranger who just never stops. He has a strong commitment to his team and to keeping the world safe; Kevin even gives up his dream path to being a professional athlete to become a Power Ranger.
Commitment isn't everything though. In one of his earliest solo outings for the team, Kevin proves himself to be one of the strongest members. When all of his teammates are incapacitated due to the monster of the week, it's up to Kevin to find the Swordfish Zord. Not only does he succeed on his own, but even when he's injured at a later date, he doesn't give up. Kevin draws up battle plans for the rest of the team even if he can't be a part of the fight.
7 Weakest: Theo (Jungle Fury)
Overall, Theo isn't a weak Ranger. He is, however, weak when it comes to the way Blue Rangers are presented in a fight as part of the team.
The Jungle Fury team channels the spirits of different animals in their fighting styles. While Theo channels the jaguar, his particular fighting style isn't as aggressive or offensive as the rest of this team. Instead, he's evasive, his fighting style used primarily for defense. Theo isn't the first Ranger to enter a fight, or even the first Ranger to come up with a plan.
6 Strongest: TJ (In Space)
TJ actually starts his journey in the franchise as the Red Ranger when Tommy chooses him as his replacement in the Turbo season. For Power Rangers In Space, TJ gets a demotion of sorts as he becomes the Blue Ranger while Andros takes over as team leader.
TJ proves himself just as valuable as a supporting player as he does a leader. He knows just what the team needs, even if he isn't the one calling the shots. To be fair, Andros has been traveling through space for a lot longer than the rest of the team, so it makes sense for him to lead the charge off Earth. TJ never flounders in his skills and always lends himself as Andros' right hand.
5 Weakest: Justin (Turbo)
It's not Justin's fault that he's one of the weakest Blue Rangers. Justin has a serious disadvantage compared to literally every other Power Ranger: he's a child.
While plenty of Power Rangers are teenagers over the years of the franchise, Justin is the absolute youngest to ever don a mask and spandex. When he takes Rocky's spot in Power Rangers Turbo, he doesn't have the same level of experience in life, or in a fight, that every other Power Ranger has. That makes him a bit more prone to rash decisions and not realizing that he might not have the skill to take on an enemy alone.
4 Strongest: Sky (SPD)
When the SPD B Squad is formed, Sky fully expects himself to be placed in the position of team leader. That doesn't happen, partly because of how much he looks down on the new recruits. The truth is, that Sky has a lot of growing to do then, but he definitely grows into a better leader over the course of the series.
Sky is just as accomplished of a fighter as the other Power Rangers on his team, but he also has a pretty great skill for a Blue Ranger: he can create force fields. That special power gives him a bit of an edge over a lot of the other Blue Rangers in the franchise.
3 Weakest: Koda (Dino Charge)
Eventually, Koda does prove himself to be a powerful hero, but for a long time, he's a bit of an ill-fitting member of the Power Rangers team.
That's because Koda doesn't entirely understand the world he's in. Koda gained the energem that would make him a Power Ranger during prehistoric times. Frozen in time until the rest of the team formed in the modern day, Koda spends a lot of time scared of modern technology, not even wanting to use the weapons and zords that come with being a Power Ranger. It takes a lot of adjusting for him to accept his new life.
2 Strongest: Tori (Ninja Storm)
Tori is the first female Power Ranger to be a Blue Ranger. She's also the only female member of her team and someone who's really into extreme sports. Tori, like most of her team, is a bit of an adrenaline junkie who happens to end up in a position to be a super hero.
Luckily, Tori is really good at being a Power Ranger. She embraces her powers quickly, and in addition to the ninja abilities taught at the academy she attends, Tori also becomes a master over water. Tori is also the only member of her team to get her Ranger abilities back after the season, appearing in a few team-up episodes - one even without her teammates.
1 Weakest: Billy (Mighty Morphin)
Billy might be the longest lasting Blue Ranger of all time with his three seasons of the original series, but the truth is, he's really not great in a fight, as viewers see often in his spotlight episodes. Billy's strengths are not actually in being a Power Ranger.
Where Billy excels is behind the scenes. He's a valuable asset to his team when it comes to broken down zords and depowered weapons because he can find a way to fix them in even the most dire circumstances. That's why he's so great as a civilian who helps the Power Rangers in the Zeo season.