Well think your dfinitions of the three may be a little off (or I'm reading them wrong.) I'm not trying to challenge you.
Ko Uchimata: In a right-handed technique your leg attacks the lower part of Uke's left inner thigh.
O Uchimata: Your leg attacks the middle of Uke's thigh. Usually lifting up along the inside of their far leg, and landing in the middle.
Taka Uchimata: Tori's leg attacks Uke high on Uke's left inner thigh -- effectively reaping up the middle.
Checkthe followingthread for videos of each of the three.
Uchi-Mata Reaping Leg - JudoForum.com
As for me, It's O-Uchimata all the time, every time.