Elevator maintenance companies

My Condo building of 30-something units (four floors, plus garage in basement) is starting a search for a new elevator maintenance company. The incumbent is unresponsive, uncommunicative and possibly incompetent. I am regularly told that they are all as bad as each other, but I would appreciate any recommendations, plus any tips on what to demand in a service contract, particularly how to incent the company to provide good service. Thanks in advance.