2 fat rows cools better than 3 or 4 narrow rows.
Copper/brass cools better than aluminum, but only if fins are brazed to tubes and not soldered with lead.
Aluminum with 2 fat rows and brazed fins will outcool an old school 4 core brass/copper, but a 2 fat row brazed copper will outcool the aluminum.
Confused yet?
Get an aluminum with 2 fat rows that is brazed and not epoxied and don't worry about plastic or aluminum tanks and you will be happy.
1987 Jeep Grand Wagoneer...new 6.5 in process...diamond block, 18:1's, other goodies...