You can use either, but in a networked environment or in a VoIP environment, ACD queues do not always work and you must use a phantom. Just keep that in mind. If it is a stand alone system, you should be fine.
Remember that Call Pilot "prefers" phantoms so anytime something doesn't forward to Call Pilot correctly using an ACD DN, use a phantom.
In Succession 3.0 and higher, phantoms do not use TN licenses.