I have the simple SPOT system that only has the 4 buttons on it (Track, Check In, SOS and "Help Needed, Not Urgent"). It's a pretty slick little unit and I have never had it not get a signal.
I looked at the fancier ones and the ones that sync with a smart phone but since I mostly use mine for backcountry camping/canoeing I didn't want to be stuck with a dead smart phone (do any of them get more then a day out of a charge anymore?) if I ever really needed it. This unit seems to get over a week out of a single set of batteries, we normally change them just to make ourselves feel better, not because it goes dead.
Edit: It's also handy for checking in on where you were when you get home. I've used mine to keep track of little honey holes of fishing and hunting. Just have it track you all day and send a "Check In" message if you find a sweet spot. Load up Google Earth afterwards and you can compile a neat little database for future reference.