whats the best radiator?

[Robo]

Copper brass should be the best at doing the intended job.
Brass for main body rust resistant.
Copper fins to absorb heat away from brass and disperse the heat away.
Alloy fins don't corrode away like copper
Probably really only used in mass today for weight saving and lower production cost.
And to be fair, externally lasts better than traditional brass copper.
But you would find copper wins at dispersing heat better than alloy.

It is constantly being "sand blasted" buy particals all the time , paint wears exposing the sensitive copper elements.
If you want to make brass/copper 1 last, then say annually .
All you need to do is remove, flush inside and out annually, let dry and lightly respray to renew protective coating.
This will if done correctly extend the life of rad substantially.
not to mention you should be flushing the entire cooling system while your at it.
Rad coolant is an enviro hazard so dispose of old stuff responsibly.
renew with mixture of recommended product and de-mineralised water only.
D-water is far better cooling and anti corrosive than straight tap water.
D-water has a higher boiling point, than straight tap water.
You could replace thermostat say bi-annually, but that's my idea of good practice while your at it.

If you decided on alloy then 1 with the proper air flow and cooling capacity is needed.

A mate of mine purchased an alloy e-bay job about 2 yrs back.
thinking thicker was going to be better, not always true.
Airflow has to be maintained if going thicker.
Product design and quality is what matters.
It leaked, and suffered insufficient air flow to cool water.
lucky for him he was able to return it as faulty item for refund.
Cheers