Saitamas power explained.

So looking at most discussion threads i concluded that people don't really know the explanation behind Saitamas power. It's understandable because it is only explained in ONEs original manga and not many have read that.

So if you want to know exactly what Saitama is you can read about it from his creator here http://www.mymanga.me/manga/OnepunchMan_ONE/56/12 or in the spoiler below:

No matter how much effort they put into it, every living being has a certain individual limitation to their growth.
A living being has a set growth limit. Grow too strong and the burden on the wielder could make them lose control like a monster that has lost their mind. That is why god has made each and every living being so that it cannot grow further that a certain degree, for their own survival and sanity. this growth restriction is known as a limiter.
However he had pushed himself to surpass his limitations and succeeded in removing his limiter.
In exchange for his strength, he became bald. And after burying my strongest warrior with a single punch, his expression had told me... of the overwhelming feeling of alienation that his strength had given him...

So yes Saitama is the most powerful being ever. That's how it was intended to be. Saitamas punch at 100% = big bang(that's what his creator ONE said in an interview)
Don't forget that his whole character is satirical, meaning not to be taken seriously, so all threads Saitama vs Superman, Saitama vs Goku etc. don't really matter that much, because the compared characters are, you can say, from different genres.
Also his regime 100sit ups, 100 push ups, so on... is just the means he used to channel his effort into evolving into the only being with no limiter and is not directly responsible for the result.