which has the most potential when put to a normal royal?
yellow belly.
Fire.
Lesser Platty.
what would you get if you did these combos?
yellow belly x fire
yellow belly x lesser
lesser x fire would this one just throw up brighter lessers?
yellow belly to a mojave
lesser to a mojave
They are all Co-Dom, so all have the same potential (50% chance per egg), then it just depends which you prefer. All of them have the potential to make a white Royal in the Super Form:
Fire - BlkEL Lesser - BluEL Yellowbelly - Ivory
I'm not sure any of the combinations you list have another name apart from maybe as Daz says the Red Spectrum (although this is debated).