Neither is nessecarily "better" then the other. Infact they are best used in conjuction: Reflectors to shoot down any and all light, mylar to reflect lost light surrounding the plant (better lower canpoy developement). But I only have one thing to say as far as mylar goes... DON'T USE IT. It's just another thing in the grow room radiating heat from your bulb. Bet use flat-white paint. It IS and always will be better