I have owned both, an '05 ST which I kept for 2 months back in 2005, was heavy on fuel and the performance felt very lack lustre, complete disappointment and my biggest car purchasing mistake

We then also had an 08 Zetec S TDCi which we bought in 2009 and sold earlier this year, this was a great car.
£35 per year tax, £200 insurance, 50mpg regardless of how you drove it and on a run 60+ was achievable, plus the car just seemed more fun to drive than the ST with a good fun chassis.
100% reliable with only a set if tyres in our ownership beyond the annual services, my wife loved it and I would recommend one as cheap fun motoring
