I have two rings, a crappy green ring and a 489 agi ring that has alot more stam and mastery on it than the green. Noone needed the agi ring, so I took it and decided to use it since the gained mastery and stamina seemed better than additional strength. This is my alt, btw, so I havn't kept up with it much.
Just got out of an LFR after being yelled at for having the ring; people were saying even a green str ring would be better. Is that true? I don't mind being wrong, but I don't recall strength having anything to do with the blood shield, just mastery and how much damage you have sustained.