Only one of the two franchises does its supporting characters justice.
Despite both Bleach and Naruto being incredibly successful franchises in their own right and both of them boasting tremendous popularity with legions of fans — there's a certain sentiment that is generally supported by everyone other than the die-hard Bleach fans that Naruto is the superior series.
Its roster of characters is bigger, plot is more ambitious, action is more over-the-top and bombastic — and it does, in the end, have more fans and bigger sales numbers.
Yet, there is at least one aspect that Bleach absolutely destroys Naruto in — and it's power levels and everything that has to do with them.
While the main protagonist of a fighting shonen anime is by the very definitions of the genre is supposed to be constantly getting stronger and stronger until he or she becomes the most powerful warrior around — it is also very important to keep the supporting characters' power levels relevant too. Because otherwise they would start to completely fall out of their places — first in fights and then perhaps even in the story itself.
Arguably this is exactly what happens in Naruto with its entire first season of 150 plus episodes having pretty much two compelling fights where Naruto himself did not participate in: Orochimaru vs The Third Hokage and Kakashi vs Momochi Zabusa.
And while the showdown between Orochimaru and Hiruzen Sarutobi was a masterpiece by all accounts, the fight between Kakashi and Zabuza, while being a compelling story arc, did last for a whole eternity and seriously struggled with pacing.
In season 2 this trend arguably gets even worse as, while side characters do in various duels and battles, their stakes are usually much lower than those of Naruto's. Even by the midpoint of the season Naruto is already almost unreachable in terms of power to anybody of his allies, with the only possible exception being Sasuke.
Bleach, on the other hand, offers an entirely different approach by having many and many of its side characters remain on a power level that is more or less comparable to that of Ichigo. This, in return, allows for much more compelling storytelling with the world and its characters feeling more alive, more dangerous and not entirely dependent on the main hero.
Kenpachi vs Tosen, Uryu vs Mayuri, Gin vs Toshiro — all these fights not only have great choreography and pacing but also play an important role in the story. Something that Naruto, despite its lengthy arcs and a long roster of seemingly capable characters never quite managed to achieve.