Mt. Abram is your best bet of those three for minimal crowding, but it is closing weekend for them, so I don't know what that will look like. If people do show up, you may experience lift lines, but the slopes are likely to remain uncrowded.
Pleasant, in my experience, tends to be very weather-dependent—nice spring days tend to draw a crowd, but if it's cold and blustery, there may not be anyone there. I've never been there with new snow to have any idea in that regard.
Sunday River will have lots of people, but they will get spread out far more effectively than either of the other two options given the amount of terrain and quality of the lift system. If I were choosing between Mt. A and Sunday River for freeskiing, I'd go with the latter and just do my best to dodge the crowds; you can get more actual skiing in even with crowds on (mostly) modern lifts. Mt. A gives you a much better chance of parking close to the lifts, though, and vastly lower skier density on the hill.
