atk ring is better if you're going to be fb'ing or ss'ing cause you always hit 100% and noone really hits physically anyway unless it a 2-hand user. Even then, a damage skill like boreas or rage have a high % rate of activating so the dex ring is pretty much useless.
I used a super +4 dex ring, i'll admit i did hit alot more with normal atks, but then again, i got my elite sdg +3 atk ring and i love it XD