What a question!
In my opinion, it's impossible to answer! What criteria would you apply to Ladyboys across the world in order to decide which are best?
Living in Thailand I probably should vote Thai (and they are beautiful..) but I remember a particularly stunning Spanish girl (Oh and a Jamaican ballet dancer..) I used to know and she has a very special place in my heart/memory.
So, my vote for the best Ladyboys is not based on a geographical demographic but quite simply this - the one you love.
How mushy is that?