We stopped using UPS years ago - their tracking system might as well be non-existant.  FedEx customer service is amazing and we have never had any problem that they haven't been able to fix in short order.  Unfortunately they are very pricey.  We have recently switched over (with much trepidation) to priority mail for less crucial packages due to the dramatic cost savings.  So far so good - but I would still use FedEx for anything crucial.