Choosing between EPO and PPO?

My wife's employer has changed and so we are changing our health insurance at the moment. Her new employer offers several plans and I have narrowed it down to Empire's EPO and PPO plans. The EPO costs about $15 per month less and it has significantly lower copay and deductible compared to the PPO. As we have no strong preferences over which hospital or doctor we use and because Empire's network is very extensive I was happy to go with the EPO until a coworker of my wife warned against it. What happened to her with another insurer's EPO plan is that, when she went to an in-network hospital for some reason, the doctor recommended her to go through certain tests. However the devices that they used on her belonged to a "legal entity" which was not part of the network! So the insurance company did not pay a dime for the costs of the tests. I think this is a very lousy business practice and the hospital and the insurance company are together in it. However, I would not be surprised if it is something very wide spread. So my question is is anyone else aware of such practices or any other reasons why one should definitely go with the PPO rather than the EPO when the monthly costs are comparable? Thanks.