It's going to be packed on both of those days due to Easter Weekend. You might have a tad bit better luck on Friday, since it's Good Friday and a work day, but you probably won't notice a marked difference between the two days.
I agree with the other posters. Both are something like a 9 on a scale of 1-10 (with Easter Sunday being a 10).
We're using that Saturday as a resort and DTD day, as I suspect all of the parks will be crowded. Friday, we'll try MK and then probably hop to another.
Based on prior experience at Easter, Friday will be somewhat lighter than Saturday, and Sunday and Monday will be the most crowded MK days. However, by somewhat lighter at that time of year that means lines for popular rides will average 100 minutes most of the day rather than 110 minutes on Saturday.