With the varying construction, a better indicator is core thickness. If core thickness is the same, one with less cores will be the most efficient, cool the best. Newer design, aluminum, allows for wider/deeper core tubes, so more of the tube area has fin contact. Also allows for tighter fin and tube spacing. So a 1" single core can be more efficient, have more cooling capacity than a 1-1/4" 3 core. The aluminum designs also often have significantly lower air restriction, so need less fan to do the same job.
Up to recently I was one who would always recommend copper, all metal, not any more. Newer antifreeze formulas are biased to protect aluminum, the main customer. When did the last copper radiator leave the factory, two+ decades ago, so why would they care? It doesn't do a good job of protecting copper, mainly the solder, commonly see bloom, corrosion, solder thinning, etc. We often travel in caravans of '80s, and have yet see a copper that will cool on par with any aluminum and have seen most of them stressed and the difference is significant. In our experience a dealer copper will not keep up with even the cheapest aftermarket aluminum. They may work well enough for some less demanding climates, but why give up capacity?
At one time, copper lasted a very longtime, not seeing that now. Could get them inexpensively repaired, now not so much, the last two we had quoted were twice what a new one cost and both of our favorite shops have now gone out of business. Now my first choice is aluminum, the only time I would recommend copper is; a nut & bolt restoration or if there is nothing available. Aluminum and plastic is well proven, can be had inexpensively, work well, see them as disposable, change them as needed, a clean new core is always better than old and crusty.
