For me personally the 2 main factors for the engine choice would be fuel consumption and driveability
I ran 30psi on my 1.6 and that suka is still on the road.But..I set it up correctly, MLS head gasket, ARP head studs etc etc.But oh what fun..
Don't know if you got the 205 GTI or the Golf GTI in both guises?the smaller motor was always considered to be the drivers option.Sure the 1.9 can grunt but I dont need that in a small light chassis.