I use the Devcon Titanium Putty. Mostly because I have it on hand. Like Ganderite, I was using their Aluminum Putty but found it to be a bit brittle. Not that it caused any accuracy problems but it would break off the at the thin edges at the most inappropriate time.
Devcon, JB Weld and a multitude of other epoxies can be used. I've even used some of those 2 part epoxies from the Dollar Store with success.
The reason I come back to the Titanium Putty is that I can put a rifle so bedded into the safe and come back to it a year or two later without worry about whether or not it's lost its zero or the bedding has shrunk etc.
I won't say there aren't other types of epoxy that won't do the same thing, just it's my experience that with Devcon Titanium Putty it's right first time, every time.