I've never personally been in March as I've been told it can get quite crowded due to various different spring break dates.
We went in May last year and it was lovely. Low ish crowds (I'm used to September which is very low but I think longest queue was about 20mins) weather was beautiful too.
Flights were reasonable (we paid £415pp M&M). We booked using DVC points though (May is the middle season & March is a higher season).