Normally, I run neither, but I will say this. I have no issues with either. I've ran exclusively shimano guts on the geared bikes I've owned. I have an XTR rear on one bike and an XT on another. If I were buying another shimano rear, I'd buy an XT based on price and performance. If I were buying a SRAM, I'd probably buy the X9 for the same reason.
If I were building a geared bike right now, I'd probably go with SRAM based on the 1:1 ratio and the rapid fire shifter availability, and it's a Chicago company.
Any derailleur will come out of adjustment sooner or later and both will snap off just as easyily under the right conditions. Just a matter of when.