I used to have made a 18.5lb square wire spring for the 1911.
Square stock springs are absolutely THE very best performing spring there is, IMO.
Used to have a source for them but not anymore; now I use variable rate springs in most of my guns.
My general preference is to use the lightest spring that functions properly. That usually is a 16.5 - 17.5 lb in a 5" gun, 18.5 or 19 in a 4.25" gun.