Those are both SS2. Gohan's is just optimized. At least that was my understanding after reading the manga multiple times. Turns out it is officially defined as you said.

This is based on?

Because Gohan's martial art skills are no where near Goku's. He never trains and he doesn't even like fighting. He beats Goku in raw power, but what's the point if he can't use that power to its full potential.

I've changed my decision, my favorite Dragon Ball character is Bulma.

Gohan is 2nd and Android No. 18 is 3rd

Not what i was trying to say.  The original writing was literally to have mystic gohan beat buu.  It was changed to have goku be the hero because he is a fan favorite and the writer of the TV series liking him.

Someone with a little more knowledge than i have could maybe explain this better, but either in the mangas Gohan defeated buu or it was the original writing in the show and it got changed.  You can look this information up as im not sure of which took place.  What i do know is they changed it to make goku the hero when it was originally intended to be gohan.

I thought he did  after vegeta lets cell reach his perfect form.

Only the true strongest Saiyan in the Universe!!

Best villain together with Frieza. Brolly and the likes of Buu are just freaking boring, they never have any sort of nuance.

Teen Gohan (SSJ) He was a pure badass when fighting Cell.
Krillin, for always taking the first Dragonball wish.

Future Gohan SSJ1 was stronger than the, albeit weaker than the present time, ANdroids individually. At least in the movie. If you go cannon then i would agree Future Gohan is not the strongest.

In the movie we see Gohan beating up Androids individually BEFORE he loses his arm. Even if those future Androids are a bit weaker than the presesnt tense ones, Gohan being stronger than them makes Future GOhan roughly on par with Vegeta SSJ1 when he faced N 18 in the present. Thats BEFORE he loses the arm.

Going fw in the story, Gohan recieves a Zenkai boost for his near death experience when losing the arm. so its safe to assume Future Gohan with one arm is stronger than Vegeta SJJ1 when he faced N18, which was the strongest SSJ1 in the Android saga before Cell.

I would put Future Gohan after the Zenkai in the power level of present Piccolo-Kami-sama, or even beyond since its showing traces of SSJ2 in the movie.