Ziskin

My personal philosophy is that you should wear whatever will get you the fastest xp. It's true that defense helps you to stay longer at a given place, but the strength bonus on the obsidian shield means you are doing more damage while you are there. So even though the defense on the d square is a bit better, myself and a lot of players choose the obby shield instead. If it were me, though, I'd go with a rune defender.