I find the neck on my Kala KA-TG to be about the same thickness as my Ohana SK-35G neck, which is thinner than some other sopranos I have played. I don't like thick necks either, and the Kala tenor feels nice in my hand.
I know what you mean about too thick, some of the cheaper no name ukes are like that... the nicest feeling ones I've tried have been the Kelii, Melokia, KPK tenors. I haven't been lucky enough to get say a Kamaka, Ko'aloha or Kanilea, but I bet those feel good, tooo! Ohhh droool!:drool: