To be more specific as a source of reference, carbon steel will hold up to 1.623 times more heat than aluminum per its weight, but often manufacturers use less carbon steel than aluminum in the construction because steel is stronger than aluminum. So how much heat the pan can absorb comes down to mass more than material. If a pan is engineered with yield strength in mind, 1.82 times more aluminum than steel would be needed. That allows aluminum to win the heat capacity prize by 19.7%.
Aluminum also transfers heat about 4.08 times faster than carbon steel. This allows it to heat up faster and subsequently cook the pizza faster. Obviously this is a good idea if you aren't preheating your pan. If you are preheating your pan, the aluminum will probably cook the bottom of your pizza too fast.
Assuming you're placing the pan in the oven at the same time as the pizza, aluminum wins in every aspect except cost, since carbon steel pans are traditionally cheaper.
EDIT: Edited for clarity. I meant to say "per its weight" not "per weight."