Western Pennsylvania employers and their workers will have more health insurance options this year after the University of Pittsburgh Medical Center's signed contracts with three insurers, but insurance experts had mixed options on whether the deals will drive down rates. Contracts with national, for-profit health insurers Aetna Inc. of Hartford, Conn., United HealthCare Services Inc. of Minnetonka, Minn.; and Cigna Inc. of Philadelphia, were reached against a backdrop of the failure of UPMC, the dominant health care network in the region, and Highmark Inc., the dominant health care insurer, to reach a new contract to cover three million subscribers. United Healthcare's deal with UPMC was disclosed on Wednesday.