Don't overlook the advantages of a VHF radio.
If you activate your PLB, the signal will go to the COSPAS-SARSAT satellite system, then to NOAA then on to the nearest rescue coordination center, which then has to decide what to do about it.
When it arrives at the rescue coordination center, it arrives as an "uncorrelated mayday," which is usually not enough information to prompt an immediate launch because false, inadvertent, and otherwise stray signals do come in.
If you registered your PLB, they'll call whatever numbers you provided when you registered it and get as much information as possible to figure out what's going on. If the contact person you provided also has your float plan for the day and your signal came from where you said you were going to be, your case can get elevated from the "alert" phase to the "distress" phase quickly.
If, however, you haven't registered your PLB, they won't have anything to go on other than your position. They won't know your name, type of vessel, nature of distress or anything else. Don't expect a helicopter to appear overhead until some sort of correlating information comes in--like an overdue report from someone back home (You do tell someone where you're going and when you'll be back, don't you?)
If you call 911 or the Coast Guard from a cell phone, you'll be able to communicate who you are and the nature of your distress, but the position information may not be precise or immediately accessible.
On the other hand, if you call the Coast Guard on channel 16 from a VHF radio in a coastal zone, their digital select calling will immediately pinpoint your location, and they can play back and enhance the audio of your radio call to make sense of whatever you're yelling into the radio. That's your best bet for an immediate launch of rescue assets who know who you are and where you are.