I've always read ちょ as "cho" because if they needed to write "chiyo" they would just use ちよ.
Now, ち is kind of the exception there, because ぎゃ, みょ, ぴゅ, etc. already sound like "giya", "miyo", "piyu", etc. because the "i" sound blends with the "y" sound. That's why they are written as "gya", "myo", pyu", etc.
(At least that's how I see it...)
January 22, 2017 at 6:16pm