I think the lip purr is the least authentic sounding turkey purr.
Some guys can flutter their tongue very well and get a good sound.
I like the gargle method because I have the most control with it and I can transition right into other calls like soft clucks, yelps, and whines without moving the call around.
Actually for just strictly purring and clucking, I like to do the gargle method with no call at all. It is very easy for me to get a feeding turkey purr by just getting my uvula flapping with a gargle and clucking in the back of my throat.