Aussie bred so I tend to say zed, but sometimes I do revert to saying zee. The alphabet is an interesting thing, according to my dad, the South Vietnamese system doesn't (or should that be didn't?) have a V intead the 'V' sound is substituted with a 'Y' so in effect Vietnam in southern Vietnamese sounds more like 'Yietnam.' H is also interesting because in French there is no H sound because most words starting with an H the second letter is a vowel so hotel is spelt (is I remember correctly) l'hotel and pronouced as 'lotel.'
So to be honest, it depends on where you were brought up and how ou were influenced, but z is pronouced zed in most British speaking countries.
