Despite all of the jokes, memes, and disses to Goku for not being a more present father, Goku and Gohan shared one of the strongest bonds in the series. We always saw Gohan's need to protect his father as a young boy, standing up to foes like Garlic Jr. and Raditz when Goku's life was at stake. We also saw Goku train and mentor Gohan before the fight against Cell, helping his son uncover his own Super Saiyan transformation. But perhaps the most significant bonding moment between the two was when they defeated Cell.
In one of the most iconic scenes from Dragon Ball Z, Gohan, empowered by Goku's spirit, released the Father-Son Kamehameha, a move that sent Cell straight to the Other World. While we have to give the Father-Son Kamehameha its credit here, we can think of several other attacks that are stronger than the mightiest move we've ever seen from a young Gohan.
10 Stronger: 10x Kaio-ken God Kamehameha
Despite not packing as much of a punch as some of Dragon Ball's most infamous villains, Hit was one of Goku's most fearsome foes, due to his ability to manipulate time. During their first fight, Goku was forced to combine the powers of his Super Saiyan Blue form with the Kaio-ken in an attempt to overwhelm Hit.
In what should've been a finishing move, Goku launched a Kamehameha Wave that was so powerful that it managed to crack a barrier created by Vados. We know for a fact that the Father-Son Kamehameha wouldn't be able to overpower this move in the slightest, given the fact that Gohan as a Super Saiyan 2 is leagues below a Super Saiyan Blue Kaio-ken Goku in terms of raw power.
9 Weaker: Solar Kamehameha
Just like the above answer, this one should be a no-brainer! After receiving an incredible Zenkai boost after regenerating from his own self-destruction, Cell returned to Earth to finish off the Z-Fighters with power that outclassed even Gohan's.
His strongest attack, the Solar Kamehameha, possesses enough power to destroy the Earth's solar system, and yet, the Father-Son Kamehameha was enough to completely push back his attack.
8 Stronger: Planet Burst
After taking one look at Goku and Vegeta, Kid Buu began accumulating energy for his Planet Burst attack, a move that intimidated Goku so much that he begged Buu to stop. He even noted that the attack possessed enough energy to blow up the Earth ten times.
With such a massive amount of concentrated energy gathered so quickly, we can't think of many attacks that can overpower this one, including the Father-Son Kamehameha, which just barely managed to overcome the Solar Kamehameha.
7 Weaker: Destructo Disc
Originally, the Destructo Disc allowed Krillin to injure enemies far more powerful than him, like Nappa and Frieza. It was often said that the Destructo Disc could cut through anything, although this really depends on the power level of the technique's user, since Krillin's Destructo Disc did nothing to Perfect Cell, and Cell's Destructo Discs were easily stopped by Gohan.
The Father-Son Kamehameha could definitely disintegrate any Destructo Discs in its path, especially if Krillin were the one to throw it.
6 Stronger: Sphere of Destruction
As a God of Destruction, Beerus's ki is more lethal than that of a Super Saiyan 2. Even a small drop of his energy is enough to completely destroy a planet. If Kid Buu's Planet Burst has enough energy to destroy the Earth 10 times over, Beerus's Sphere of Destruction has enough energy to destroy the planet a million times over.
It's so strong that even after effectively nullifying the move, Goku was left with no energy at all. No matter how strong Gohan's Father-Son Kamehameha is, it doesn't hold a candle against an opponent who could literally flick a Super Saiyan 3 away with a finger.
5 Weaker: Supernova
The Supernova is an attack not only favored by Frieza, but his older brother Cooler as well. Since Frieza learned to tap into the powers of his Golden Form, we haven't seen this attack as much, but we first saw it in action when he used it to destroy Planet Vegeta in seconds. Although Gohan's Father-Son Kamehameha didn't destroy the Earth, it did make a pretty impressive crater, and the fact that it managed to push back Cell's solar system destroying Kamehameha definitely means that Frieza pre-Dragon Ball Super wouldn't stand a chance against it.
Even Super Saiyan Goku single-handedly managed to repel Cooler's Supernova in the film Dragon Ball Z: Cooler's Revenge, so we can confidently say that a Super Saiyan 2 could this with their eyes shut, even if the Father-Son Kamehameha wasn't utilized. Now, if Frieza actually uses this attack in Dragon Ball Super in his Golden Form, there might a problem...
4 Stronger: Father-Son Galick Gun
During the Cell Saga, it was clear that Goku and Gohan emerged from the Hyperbolic Time Chamber as the strongest father and son Saiyan duo around. For a long time, we'd never seen Vegeta lend Trunks the kind of support that Gohan got from Goku, mostly due to the fact that Vegeta was very much still a jerk during the battle with Cell.
When Trunks made his stand against Future Zamasu, Vegeta stood by his side as the two unleashed a combined Galick Gun that was fierce enough to push back Zamasu's Holy Wrath attack. With Trunks unleashing the full power of his Super Saiyan 2 form and Vegeta giving it his all as a Super Saiyan Blue, it wouldn't be a far-off claim to say that their combined power would be more than enough to overpower a Father-Son Kamehameha at the time it was originally used.
3 Weaker: Family Kamehameha
The Family Kamehameha was a combined Kamehameha Wave used by Gohan, Goten, and Goku, all in their standard Super Saiyan forms during their final stand against Broly in the movie Broly - Second Coming. Due to surviving a near-fatal defeat in his first non-canon film, Broly returned with enough power to fight almost on-par with Super Saiyan 2 adult Gohan in his Legendary Super Saiyan form.
Since Gohan wasn't as strong here as when he fought Cell, it's safe to say that Broly wasn't stronger than Gohan when he fought Cell. The only reason why the Family Kamehameha was able to finish him off was due to the barrier that Trunks created to prevent Broly from feeding more ki into his Omega Blaster. All of this to say that this attack doesn't pack nearly as much power as the Father-Son Kamehameha.
2 Stronger: Thunder Flash
If you skipped Dragon Ball Z's filler episodes, then you most certainly have never heard of this move or its creator, Pikkon, the deceased hero from the West Quadrant of Universe 7. During his battle with Goku during the Other World Tournament, Pikkon used this attack to knock Goku flat on his bottom twice.
We'd already seen in previous filler episodes how Pikkon could dispose of someone as strong as Perfect Cell in seconds, something that Gohan managed to do only with the Father-Son Kamehameha, and even then we know how difficult that was! With Thunder Flash being Pikkon's ultimate attack, you can be sure that it would easily overpower a Father-Son Kamehameha with ease, given how strong Pikkon was shown to be. Don't let Dragon Ball Z Budokai Tenkaichi 3 fool you by the fact that this move can't be used in an in-game beam struggle.
1 Weaker: Triangle Dangers' Beam
Universe 9's Trio of Danger consisted of the wolf brothers Bergamo, Lavender, and Basil. All three brothers possessed their own unique abilities but weren't particularly strong. As standard Super Saiyans, Goku and Vegeta were able to give them a run for their money. Pushed to the edge of the arena, the brothers were forced to rely on their ultimate attack, Triangle Dangers' Beam.
It goes without saying that although this attack would've given Z-Fighters like Krillin or Tien a hard time, it would be nothing for a Super Saiyan 2 to handle. We're sure the Father-Son Kamehameha would tear right through it just like Goku and Vegeta's Final Kamehameha did.