Kamehameha for Gohans first form!

[Cold Steel]

KHH is more powerful.

Gohan learns the KHH after he becomes a Super Saiyan in the Hyperbolic Time Chamber in the show. The way it is in ESF is a representation of that.

You need to watch the saiyan saga again oO

 

[Rocky]

You need to watch the saiyan saga again oO

I think you're confusing masenko with KHH, the translation in the saiyan and namek saga's were way off.

 

[Ravendust]

Yes, it's fairly obvious that he's using Masenko because of the beam colour and the charging/firing position. He says KHH because it was dubbed by Pioneer (not FUNimation) who didn't have a clue. They gave Tien Piccolo's limb regeneration after Nappa blows his arm off for example ("You just wait 'til it grows back!")

You need to watch the Saiyan Saga again.