I'm a pretty wordy person, so even the custom ones aren't enough for me. 90% of the time I just use one that says "Very good" for people know I have a Watch and understand that basically means "Message acknowledged; not near my phone right now, so expect more detail later."
I've used the yes/no/or-answer a few times, but generally the brevity and scarcity of responses available with the Watch limits that function for me. For me, the usefulness of the Watch is more about making sure I get messages rather than send them.
I've used the dictate function a fair bit, though, and it's useful for when you need to be hands-free.