I think I prefer La Casa in Shadyside, but sometimes it's nice to have a change of scenery.
Ibiza is hipper (better located, more high-end ambiance, and, yours truly notwithstanding, trendier customers), but its food is not as satisfying as La Casa's. The proportion seemed just a tad off, leaving me feeling hungrier than a meal at La Casa with the same number of dishes.
Bottom line: I think I just want a bigger bang for my buck.