Again its really personal choice whether you want to modify your car or keep it standard within reason
Obviously the ZVH retains most of the CVH originality where as the Zetec is completely modified
Performance wise i dont know that there would be much of a difference but obviously the 16v would be better revving
The reason i went for full Zetec was to be different and also i really wasnt happy with the ZVH conversion. Just never felt like a proper engine, i know that sounds silly but its only my opinion. I always had it in my head that it was a botch job!