NavList:

I would light off my EPIRB and let it tell people where I am now, as well as where the raft is going to be once the wind and current move me off the initial mayday position.  Of course if you manage to bring a handheld Sat phone with you (built in GNSS) then you can just ring up the RCC and tell them where you are in addition to the EPIRB.  On most boats/ships, even if you bring a GPS aboard the raft, the required radio is a VHF that isn't going to go very far so knowing your position isn't all that helpful to the rescue assets as you still need to communicate that information to them.  The EPIRB is the best thing for this.

As to the original post, the saying is to use ALL means to determine position.  So if you have a sextant and a GNSS, then you should be using one to corrobrate the other in the open ocean.  When near land, you use the radar and perhaps some visual bearings as well.

Jeremy