I used the inreach this summer in some remote areas, and it got messages out within 5-10 minutes every time. I'd trust it in an emergency. It has more features than the SPOT and, as Nessles wrote in his recap, the service plan on the inreach is much more user friendly. It's also very waterproof - I unknowingly had it in my PFD pocket for a while and it works great. Unless you plan to drop $500+ on a full Sat phone I'd recommend the inreach.
The inreach smart phone app is also really cool. If you have your phone with you it'll broadcast a GPS signal to your phone and your phone will bring up a map of the area you are in - which would be super helpful if you were lost. As you can expect it murders your phone battery so you wouldn't have it very long.