The Nexus 6 is a very expensive phone compared to the last few Nexus devices. However, it also makes fewer compromises. If you are close to pulling the trigger now that supply is starting to (kind of) catch up with demand, T-Mobile has a deal going that might push you over the edge—it's brought back the $48 discount code for both storage options.
The 32GB Nexus 6 sells for $649.92 on T-Mobile, either up front or on a payment plan. Using coupon code NEXUS6DEAL, you get the device for $601.92. The 64GB version drops from $699.92 to $651.92 with the same coupon code. This is the same deal that was available on Cyber Monday, but it requires the above code this time.
T-Mobile only carries the blue Nexus 6. If you desire the cloud white, you'll have to go to Motorola or Google, but that one is still constantly sold out. Also remember T-Mobile doesn't do contracts, but you need to either be a customer or set up a line to buy from the carrier.