Mormons tend to be more professional and likely have networks they can use for communication, out of the control of the LDS.
The other important difference is each religion's claim to authority. They think they "had" a prophet who gave them their commands. The JWs think the current GB are speaking for god so JWs tend to be more controlled IMO.
Finally, the LDS are concentrated in Salt Lake City especially so getting a large group together has less logistical problems than with JW's who are not really concentrated in any one area.
Attacking their tax free status for discrimination but I personally don't believe it will happen - the evangelical base in the US is too large and too powerful politically to make it likely. The only way I can see it happening is if the Republican party completely implodes and the religious right ends up isolated and on their own.
Ultimately though, it's changes in general public opinion that will be their undoing. They will be increasingly seen as backward and will change of their own accord. Just as they abandoned their claim that black people are inferior, this will be given up too.
But that doesn't mean they won't find ways to promote their own ideals, however unfair or judgmental they are.