SSJ2 > SSJ1 (and all form) > Kaio-Ken > Oozaru > SSJ4 > SSJ3
Prove me wrong. I'm not even counting Gods form because it's just swap color
SSJ1 > kaio-ken > SSJ3 > SSJ4 > Oozaru > SSJ2 > SSJG
Gohans transformation to SSJ2 is one of my favorite scenes, but the form itself looks exactly the same as SSJ1, just with lightning. All the other transformations bring something new to the table.
But Gohan's hair IS different. Goku's too, to a much lesser extent. Sure Vegeta's doesn't, but what the hell are they gonna do? It's much, much better than Goku the Hedgehog, and SSJ4 just looks straight dumb.
SSJ2 > SSJ > Kaio-ken > SSJB > SSJG > SSJ3 > SSJ4
It's a very miniscule difference, and in combat it isn't even visible. also i forgot, i would put Ascended Super Saiyan between kaio-ken and ssj3. I actually thought it was SSJ2 the first time i saw it, and was disappointed when the real SSJ2 form was just a slight hair strand rearrangement of SSJ1.
Goku went full powered ssj too, but he didn't use it against cell because he knew he'd be too slow. It was also heavily implied that vegeta could also go full powered ssj, but he knew if its limitations.
>I'm not even counting Gods form because it's just swap color
SSJ1 > SSJ3 > SSJ2 > Kaio-Ken > Oozaru = SSJ4
I rate ssj3 so highly because it is a total failure. It's an attempt to capitalize on gohan's style of improvement with ssj2, but it is effectively like a kaio-ken multiplier for super saiyan because no one knew how to really improve on ssj2 meaningfully.
It powers you up but it burns you out. I also loved that they basically threw it out there right away to show that a new standard power up wasn't going to save their ass in the end. The desperate trump card was the first move and it failed horribly.