I've used both, but fortunately I've never needed either. I originally went with Global Rescue because they'd been around for awhile. When Ripcord came out, and they were offering comprehensive trip insurance I went with them....sort of one stop shopping. However, now that Global Rescue is offering trip insurance, I think you'll be well served with either.
The point I think is to go with something. In my opinion, it's relatively cheap compared to the huge benefit if you happen to need it.....
As usual, my $0.02....