i am a bit confused ether using laminating or infusion for R.C airplane ,

what i believe ( correct me if i am wrong ) is having the minimum resin in the product is the main reason to have it with light weight !

1- laminating by using the(Breather Layer Cloth) will absorb the extra resin during vacuum process.
2- infusion also absorbs extra resin by keeping the vacuum line few minutes open after closing the resin supply .

so ,, what would be better ?

That is a simple question with a complex answer.
If you are planning a monolithic laminate, infusion will likely give you the lighter result.
But RC planes are mostly done with sandwich construction methods. And this is where wet layup comes into play. If you want to infuse a sandwich structure, the core does have to have some resin flow propertys, wich always result in additional resin uptake. Wet layup doesn't need this, you could use "solid" foam. Combined with very light carbon cloths and minimum resin application, this will result in ultra lightweight structures.