I dont show my girl, and wonder whether to a certain extent the lead is personal pereference, and what works for your dog? If a lead different to what most use makes your dog more comfortable, and the dog moves better in it then they will probably give a better overall impression? But I'd be interested to hear the opinions of the people who do show on this, as I have very little experience to draw on.
But...I've noticed though that a lot of the show dogs use a fine lead that has a large open loop (to go round the neck, that can then be drawn back around the shoulder of the dog when it is stacked). There is then a 'toggle' that can be pulled down the lead to make the open loop smaller for when the dog is moving. They look really nice, especially the leather ones.