Other than that of Ichigo vs Ulquiorra, there are a lot of decent Arrancar battles. However one stands out above the rest for me. With plenty of action, emotion and power struggle. It was a battle with high intensity and kept me on the edge of my seat.
Ichigo vs Grimmjow
There is just something about two OP characters confronting each other that is deliciously awesome and rather satisfying as they duke it out for the title of strongest.
What was your favourite Arrancar battle?