Just back myself...was there March 9-15. I'd say it was fairly crowded, but certainly manageable. The main things to worry about crowd-wise is spring break and the week before and after Easter. Since I was there spanning part of two spring break weeks, it was interesting to see that a lot of the northeastern schools seemed to be off the week of March 6 and more midwestern the week of March 13. I'm sure that's a great generalization, but ... There was also a large cheerleaders competition during the period I was there, but I suspect that goes on quite a bit with different organizations.
Also, we're now in the week before Easter. I would expect the parks to get very crowded this week (9 and 10 level at times); more so towards the end of the week, with the big crowds continuing well into next week. While the spring breaks last week and the week before were mostly college breaks, the Easter break will mostly be school age breaks.
In 2017, Easter will be April 16. If I was planning a trip then (and I might), I'd be inclined to go the second half of March. The college breaks should be over and the Easter break will not have started.
But, these days it seems Disney is always busy...