I can confirm that the Verizon iPhone 6 is also unlocked. I bought one today at the Apple store, and just to be safe, before I even turned it on I removed the verizon sim card and threw it in the trash. I then put in a T-Mobile SIM and restored from backup and confirmed that I was able to make calls and use LTE on T-Mobile. I then put in an AT&T sim card and did the same thing.I said every VERIZON phone is required to be unlocked. It was the condition for them to get spectrum. This is the only carrier required to sell unlocked phones. Even their "on contract" phones are unlocked.
So my conclusion is that both T-Mobile and the Verizon versions are unlocked. I prefer to have the Verizon version because as far as I know the T-Mobile version does not have built-in CDMA capabilities so whereas the Verizon version does. This would only matter if you ever want to use the phone on Verizon, or if you want to sell it on ebay to people who have Verizon as their carrier.