Most powerful technique in the series

[Godo]

Even though the Genki-dama can be a very powerful technique, it's power depends on it's range from where it collects energy and also on the amount of life within that range.

If I have to mention a technique which is both very powerful and also very bad ass, it would be the self-destruct attack, where the user concentrates all his energy to his core and releases it at once, draining his body completely. Pretty much beats the Kiko-ho in every way.

[Bussani]

And Shin kikoho cannot be the strongest attack or else everyone would have wanted to learn it.

Not necessarily. Kame sennin said that the Kikoho was far more powerful than the Kamehameha, but no one ever went out and learned it. Probably because he also said that it's a terrible technique that reduces your lifespan and should never be taught...

If I have to mention a technique which is both very powerful and also very bad ass, it would be the self-destruct attack, where the user concentrates all his energy to his core and releases it at once, draining his body completely. Pretty much beats the Kiko-ho in every way.

Badass yes, but it has a pretty lousy track-record for actually being helpful.

[Goku100xKamehameha]

Genki Dama?

It's the original name for "Spirit Bomb".
"Genki" means good spirit and "Dama" means ball.

[Titan]

Not necessarily. Kame sennin said that the Kikoho was far more powerful than the Kamehameha, but no one ever went out and learned it. Probably because he also said that it's a terrible technique that reduces your lifespan and should never be taught...

That's just BS.Training in the rosat also reduces your lifespan.Obviously, everyone would gladly take that risk to easily beat cell.
In fact,kikoho is dangerous, because it forces you to use almost all your ki and using all of your ki can kill you (Vegeta vs majin Buu or Tenshinhan vs Nappa),but Tenshinhan is able to control this dangerous technique very well.There is no reason why the others couldn't do it as well.
Plus,Tenshinhan even uses the kikoho to open a small hole and protect his friends during Goku's fight against Piccolo jr.
It is always the same story, mafuba can kill you if you aren't strong enough or if you haven't enough ki control,later on, Kami and Piccolo Jr easily use it without risking their lifes.

[Piccolo Daimao]

That's just BS.Training in the rosat also reduces your lifespan.Obviously, everyone would gladly take that risk to easily beat cell.

Where is it said in the manga that training in the ROSAT reduces your lifespan?

[Titan]

Where is it said in the manga that training in the ROSAT reduces your lifespan?

Two days inside the Rosat=2 years outside,obviously you become older faster reducing your normal lifespan in the Earth.

[Piccolo Daimao]

Where is it said in the manga that training in the ROSAT reduces your lifespan?

Two days inside the Rosat=2 years outside,obviously you become older faster reducing your normal lifespan in the Earth.

If you think about it that way...but, in my opinion, it doesn't literally reduce your lifespan. It doesn't mean you miss out on a year of life or anything, since you're still experiencing it within that room. You're just experiencing life in a different world where time works differently. I don't think it literally takes off a year of your life or something.

[Titan]

If you think about it that way

Yes, that's my opinion. You are aging faster, so in the long run you will have less 2 years than a guy who lives/trains normally in the Earth.

[ssj5goku]

How about the Devilmite Beam if that have been use on Frieza or Cell they would be kill instantly no matter how weak you are.

[dbgtFO]

How about the Devilmite Beam if that have been use on Freeza or Cell they would be kill instantly no matter how weak you are.

Bussani already did on page 1

Surprised no one has said this one yet:

Akumaito Beam [Devil-Mite Beam]
First Appearance: Chapter 104
Category: special
People: Akkuman
Special Characteristics: A beam that expands the evil that everyone has in their heart, blowing the opponent to smithereens. After touching his fingertips to his temples and concentrating ki, he launches a swirling beam at his opponent. Those hit with the technique are wrapped in sinister light, and explode. However, this attack doesn’t affect those without an evil heart. This is Akkuman’s secret weapon that he fired in order to counter Goku’s strength, during their battle in the Devil’s Toilet, a special ring in Uranai Baba’s palace. (Daizenshuu 2, p.205)

Instant death to most people. The only evil opponents who might survive it are those who can survive exploding, like Cell and Buu.

[Savage68]

Where is it said in the manga that training in the ROSAT reduces your lifespan?

Nowhere, because it doesn't.