It really depends on what you want to do. There's a TON of gaffs out there and an infinite number of way of how to present them.
For me, I'm only ever going to use double blank gaff cards for performances. Only because I'm not a fan of presenting face cards (honestly, how an one relate easily to a king of hearts...or an ace of spades...or a 3 of clubs). I'm much more a fan of audience involvement and having them use signatures and their own drawings for a more 'personalized' approach.
But that's just me