Great qusetion! This is a subject that I contemplate every night in the dojo.
I try to use inflection, tone, volume, and duration as techniques to both entertain and motivate. Wanna keep a 10 year old motivated? Monotone ain't the way! Want to get your students into that "Glare in the eye" mode? An energetic count is a great tool.
I love to end up with a big, deep, long final count: Juuuuuuuu.
To the contrary, I noticed that Sensei Robb in Sacratomatoe (sometimes) uses a final count of "Yameaaaaaay" instead of 8, 10, Hatchi, or Ju.... which, though completely different, is really quite cool. Robb Sensei is one of the kindest, most effective Sensei that I have met, by the way, and I respect him and his teachings. There is some really cool Uechi going on in Sacramento!