anything gps is definitely more reliable than vhf or cell(although cloud cover can cause problems) but i know like me some of you cant afford to have it all.......my pick since i could only really get one at the time was a dsc enabled VHF radio with gps.....has the ability to send continuous distress calls with updated gps locations to the coast guard or other dsc enabled devices at 6W (STANDARD HORIZON HX851).....this is decently powerful at 6W and if your in an area with other boaters the call can be forwarded....
i think a lot of people discount the use of a cell phone as a backup comm device.....I have done trips with other Islands up to 10 miles offshore and still received cell service!....especially waterproof models or the iphone which it seems like everyone has in a lifeproof case....great for videos and saving lives
honestly though everyone has to remember SELF RESCUE is the best kind of rescue!!!!! be prepared to get yourself out of trouble because obviously this is your best bet!
-Jeff