I've looked at them all, and I can't remember if Predator had multiple site displays or not.
I think I tried NR3 a while back but it was too slow on my web connection when it updated multiple sites, whcih is why GR3 doesn't do it.
GR3 is the best for most things, but it takes a while to get used to it. I need something to work in a room where several people might be looking at it, and GR3 tends to confuse some of them since they are not really techies or weather junkies.
Predator has a better visual 'pop' to it for those types of folks, but I don't know if it's as accurate as GR3 where it matters.
What I'll probably do is download the trial versions of each once we get closer to storm season again and give them a run for their money.