Which wiring do I need?
 

Got a thunder power 6.5T motor going into a sky toro 120A esc. Which wiring is best to use?

12 guage

Cheers pal. Will that be ok for power supply as well?

14 gauge looks better is half the weight and is easier to solder if you want my 2 cents

Will effect the power from the batteries?

I still have to back the slipper clutch off.

13 awg
 

I've started using 13 awg on most the buggies I wire up. I've done mine 2WDs and 4WDs and some friends. The current loss with the thinner cable is so little it isn't worth worrying about.
13 awg is so much easier to get a neater install.

I use 13 for buggys too. A lot nicer to work with and keeps things neat and tidy. Power loss is negligible and mine don't get warm. (I'm an Electrical engineer by trade :)