Koyo radiators have a very good rep and I currently own 3 aluminum radiators in different vehicles. The copper cores also have a very good rep.
As far as where they are made:
Where are Koyorad radiators manufactured?
Koyo manufactures four different types of radiators:
OE Aftermarket Plastic Tanks/Aluminum Cores (most common)
Design: Japan and China
Manufacturing: Indonesia and China
OE Aftermarket All Aluminum (Toyota Sienna, Lexus RX, etc)
Design: Japan
Manufactured: Indonesia or China
OE Aftermarket Copper / Brass (select vehicles)
Design: Japan
Manufacturing: Indonesia
Racing All Aluminum Radiators (select performance vehicles)
Design: Japan and Indonesia
Manufacturing: Japan and Indonesia