>>...the benefit of using Verizon is the line access discount you get by using their device payment plan.  If you order directly from Apple...there is no guarantee that Verizon will still offer said discount to you...

I spoke with a Verizon customer service rep about this. She confirmed that buying the device via another source (i.e., Apple, etc.) results in the loss of the the 'line access discount'. (This is worded as "$25 SP DEVICE PAYMENT DISC" on my monthly bill.) That made my decision easy; I paid the balance on my existing device (after arranging to sell it online) and then ordered the 6s Plus through Verizon.