Actually, there are two answer to your question.

Best heat rejection, Huper Optik 20 (which allows only 20% of light to enter the glass)
This will block out a lot of heat. and it is illegal. And being only 20%, it is very visible that it is illegal.

Second answer, which tint has the best rejection while being legal...

Most glass installed on cars are approx. 70-80% clear. So by installing any tint will almost make your car illegal by JPJ standards. What this means is that you can only install (maximum), 90% VLT for the front, and 70% VLT tints for the sides.

So, you are left with 3M Crystalline 90 for the front. and Any brand (3M, HO or Vkool) that has 70% VLT for the sides. The rear, you can use VLT 50% tint.

There’s no tint that can reject 90% heat. The only tint you can legally apply to your car is 90% front and 70% front side and 50% rear. The car’s glass is NOT transparent.

After inspection sure got saman to pay, like rm150-300, depending on type of reason.
Mine was saman due to installing HID on my old waja, as ori halogen waja is really less light. Paid rm200 summons right after inspection at JPJ wangsa maju