Are new aluminum radiators better?

Keep in mind that the core of a "brass" radiator is copper. Copper is a far better conductor than aluminum. It's still pretty much apples to oranges as most aluminum radiators have a different core density which is optimized to aluminum. End result is both work just fine when properly sized and in good working order. An aluminum radiator is lighter, but once you fill it up with water the difference is small, especially if it has more rows and holds more water. Aluminum is a LOT cheaper than copper. That's why most OEM radiators have been aluminum for the last 30 years or so. Copper/brass radiators can be easily repaired, aluminum, especially epoxy set cores, not so much.

Bottom line, a new aluminum radiator will probably work better than a 50 year old corroded up copper/brass unit. But a new copper/brass radiator will probably also work better. Aluminum replacement radiators are readily available and affordable. And if it gets you back on the road, isn't that the point.