longer term, shimano lasts longer. I had 4 XO blackbox r.mechs before I gave up & went back to XTR. the parallelogram is so close to the main mounting bolt section, only takes a small knock & its game over. do the same with shimano, will create more play but they still work. (pretty rocky around here, rock impacts are a normal daily occurance, espically after recent heavy storms cutting up the trails)
my friends sram shifters lasted 3yrs before the inards exploded. I've got 7yr old never cleaned jalopy LX shifters still going strong (hell the shifter cable rusted & snapped but the shifters are fine.)
so yeh, just my experience, but I'm sticking with shimano. Dont doubt the sram Vs shimano thing will run & run... whats the smiley for "whaaaateveeeer" again?