my personal preference is aluminum. chrome holds the heat in and i run a SB Chevy 400, .030 over so i know about heat issues, they are known for it. you can't match the good look of aluminum either. aluminum also keeps valve noise to a minimum. as far as gaskets, i like the rubber with steel core in them. i've had to take my covers off a few times for adjustments and they seal right back up, no leaks, no sealant.