The flat ground Endura will cut the best out of the 3. It's also the least expensive, and easiest to sharpen. It has a full steel frame.
The regular Manix, with the full steel frame and G10 handles, is an incredible value. US made from premium materials, with a lock that functions similar to the Axis lock but is powered by a thick coil spring, for under $100. It is also easy to carry and the handle works very well for extended use.
The Griptillian has a hollow plastic handle, and a lock that is dependent on two tiny wire springs. If one breaks, the other will soon follow. If you're out on the water or in the woods, that could be a problem. Benchmade will fix it, after you mail it back to them and wait a while without your knife.
I would get the Manix or Endura, the Grip' is a poor value compared to the Spydercos.