Well my favourite is the thicker ones thats on my fender
I dont like the thin ones, because I think that the thumb
gets a very awkward position.
I dont really know what the thin necks are for, but
I heard something about them being faster, which
I find totally inaccurate.
My experience is that I tend to miss some tones or
just be slower, since you cant get a good firm
grip around the guitar.
I guess that depends what you usually play with,
but I vote for the thick.