Here's my $0.02 on skiing in Vermont in March/April:
It's hit-or-miss, almost completely dependent on weather trends and the season's snowmaking and grooming efforts. I've had awesome skiing over Easter at Okemo, Mt. Snow and Stratton. Last season's late bounty made for powder days at Okemo over said weekend, and there were no crowds to speak of.
This season, Peak Resorts has invested a lot of money into Mt. Snow's snowmaking system, and it's one of the best in the east these days. When I skied there over Thanksgiving this past November, they were able to lay down a thick, consistent coat of man-made snow with ease, quickly recovering from rains and thaw earlier in the week. It was impressive, a marked change from my previous experiences at Mt. Snow. During that time of year, the conditions at Snow were better than at Stratton or Okemo, due in large part to the new capital investments in state-of-the-art snowmaking.
And Stratton and Okemo also have great snowmaking capabilities. That, combined with this year's ample snowfall, should make any visit in March or April a fairly safe bet. You may see some scaling back of lift ops as seasonal employees are let go (that's POWDR's approach for Killington, as they try to bring the resort back into the black), but you'll also see some fine conditions and much less crowding than in peak season.
Full disclosure: I don't work for any of the aforementioned resorts - I'm just a happy customer.