Also notice that the evaluation of EL expressions is very fast, so EL can be used in a production system. On the other hand, zscript is suggested to use only in prototyping or quick-fix.
Link
So do not use 1)
2) can be faster, slower or as fast as 3) depends on your impl.,
but to be faster may takes much time and so 2) isn't a really good idea.
3) is usually the best, cos a zul file is much more readeable then java code
and GUI logic and GUI structure are not (that much) mixed up.
To choose between MVC and MVVM read this.
If you think it makes sense to mix them, there should
be no problem with the framework.