MARVEL
Best Hero= IRON FIST
Worst Hero= IRON FIST
DC
Best Hero= THE RAY
Worst Hero= THE RAY
My explanation for this claim is simple. Both character concepts are just flatout incredible.
Iron Fist is the champion of a warrior people who treat Kung Fu like a religion and he is the Champion of one of the most powerful Elder Gods in all the Marvel Universe. Shao Lao the Undying Dragon literally is the polar opposite force in power to The Phoenix. He can channel this Gods powers and uses it in his own brand of Kung Fu...let that sink in for a second. He turns a Gods Magic into a martial arts style. He can heal, punch out Thor (yes he oneshotted Ragnarok), create illusions, channel this force into projectiles to make them explode, and etc etc etc. However, he is written horribly, they job him simply because he's less established than other heroes, and they overall have ZERO real villains for him. He fights super powered pimps and F-list villains.
The Ray (Raymond Terrell Ray that is...)has complete mastery of all forms of energy and is the more powerful son of an Original Golden Age A-Lister. He had a redhot run from 93-96, a visual style so unique and dynamic its never been used for ANYONE else in comics, and he's even taken out heavy hitters like Superboy in one shot. He can create illusions, move at light speed, turn to energy and back which also heals him, absorb radiation and energy and redirect it magnified incredibly, shoot blasts, fly in space, create solid light constructs, create shields, etc etc etc. The dude should be Green Lantern tier cosmic power and he serves Miss Waller herself as a government hero for Freedom Fighters. Given he is the ONE superhero at her beck and call who can stand toe to toe with Superman in a fight on equal footing who can produce Red Sunlight to turn the tables completely in his favor he should be a power player. He is literally one of the most powerful and pedigree-ed heroes in the DC universe.
However, he has no real villain, he was sidelined due to being thrown into too many dying comics and oversaturating him in them in an attempt to save them. Worst of all he stopped having his unique visuals drawn for him during his late DC reboot before New 52 and the current Ray in New 52 isn't even him, looks terrible, and even admits to being just some dude going by the REAL Ray's name...
TLDR
The Ray and Iron Fist are both the best and worst these companies have. Most potential and completely horrible execution of their concept's ideas.