Not sure what capabilities you want but if you want reliable, simple and no subscription fee, I'd recommend the ACR ResQLink Personal Beacon. You buy...
First airplane was a Skyhawk. Now have a PA 14 Replica (Wag Aero Sportsman 2+2, O-360 Angle Valve, 26" Tires) and love it. Bought it in Feb 2013 and put it on Clamar amphib floats in June 2014. A Catto 82/46 will go on in spring of 2015.