As far as what fills faster than others majority of the year: (a) Grand Villas at any of the resorts that have them; (b) at Boardwalk, preferred boardwalk view and lower point cost standard view; preferred pool or garden is usually open even at 7 months for the majority of the year; (b) at AKV, concierge rooms and possibly low point cost value rooms; savanna view is usually open at the 7 month window; (c) at BLT, MK view and lower point cost standard; (d) Beach Club and Wilderness lodge villas tend to be difficult at 7 months because with fewer rooms than others they get filled faster; (e) SSR is usually open well beyond the 7 month window and OKW very often is, but at any time of year you should never assume it will be easy to get something if you wait well beyond the 7 month window to reserve.
In additon, the three times you mention are not among those majority times of year and are instead very high demand times. For Christmas week you should reserve 11 months out because otherwise you face the risk of waitlisting and then hoping to get anything; if by April you mean one of the two Easter weeks you face a similar problem as Christmas although usually if you call 10 months out you can still have success; for other spring break weeks in April you can wait longer before reserving but not much and the same would be true of Presidents week in February.
