I noticed Myoplex is much more filling (I used Myoplex Lite).
The lite version had the same kcals and protein as OptNut (if memory serves) - yet was much more filling, so it fit in well as part of a meal rather than feeling like all I drank was a glass of flavored milk.
It is however, much more expensive. A box of the packets came out to (I think) close to $1.50-2.00 each, where a tub of ON, the servings are roughly about .40 each.