I went through this exercise a few months ago. I live at the edge of the Frank Church RONR wilderness and being 64 with no cell service, I bought an ACR (not the aquaversion) over the SPOT II for personal safety reasons. It is more expensive, but it is US made and what the USCG uses. The SPOT II is Chinese with "spotty" issues in workmanship, repair, and reliability. The messaging service is less expensive with the ACR and it works without any subscription for the emergency locator beacon. I chose the SARLink PLB since it is still good for limited dunking (good to 16 feet), but serves me for those hikes alone as well as the rafting.
The ACR has both GPS as well as the 406 MHz satellite location fix and the 121.5 radio beacon for local ID to air and ground search crews.
Do the web searches and see for yourself. My research indicated that the SPOT II was on average a 3 star versus the ACR 5 star. Buy it through REI and you get approximately a $50 rebate at the end of the year for members.
Good luck on this - some earlier threads in Gear Talk also.