They mean exactly the same thing (at least wrt JWs).
Perhaps the only difference would be the context in which you're using whichever term:
If I were an academic writing a paper or giving a talk, I would call JWs a "high-control new religious movement."
However, whenever I casually talk about JWs with people, I refer to them as a "fundamentalist doomsday cult."
I have yet to meet anyone who disagrees. . . . .