Duratec definately, a standard ST 150 Fiesta engine will make about 195hp just by removing the inlet, fitting throttle bodies with a good management system (I'd recomend a Pectel T2) and a good exhaust. The lengths and diameters of the primaries and secondaries are key to getting the power and low down torque. I'm fairly sure you don't even need to touch the bottom end. Plus the fact that people have been putting Duratecs in Escorts for years so the parts to carry out the conversion are readily availible.

On another note, the Duratec is a lighter unit because of its aluminium block, the other two are cast iron.