the viscous one is good, but it gets pretty damn close to an uprated rad cos it's thicker and the viscous fan doesn't move as it's bolted to the engine.
On mine, the fan has skimmed the back of the rad slightly, but I did have a knackered engine mount.
A well setup twin electric fan and cowl will be slightly better overall than a viscous as it's cooling is linked to the coolant temp rather than engine speed.