My original reply was removed, as Tom's Guide is checking into the influx of ecobee comments, so I'll try to repost my thoughts here again.
I had held off on getting a Gen 2 Nest for a couple years, as it was certainly due up for a refresh. While I waited, I found the ecobee and it was definitely the right thermostat for me for a couple of reasons:
1 - Room sensors. This is the #1 differentiator between the Nest (and any other smart thermostat) and the ecobee. If you're spending upwards of $300 on a thermometer, I assume you have more than 1 room in your house. And often times the thermostat is not in the most important place (its in a hallway or dinning room, etc). If you want to make sure your newborn is comfortable you have to guess to over/under heat based on how their room feels. This should be nothing more than a software update for the Nest, so I don know why they do not add the feature..but even if they do, you can get the ecobee and 3 sensors for the same price as just this new Nest Gen3.
2 - Homekit support. I know this one isn't for everyone, but it certainly was important for me. I use a lot of apple products between my wife and I and, in her case, its the only way she isn't overwhelmed by technology. The beauty is there is nothing, other than again software, that prevents the ecobee from being used by other systems. It has an open API and is integrated with things like IFTTT, etc. So its a bit more "future proof" as you cannot get HomeKit certified unless you meet rigorous security standards.
Which brings me to 3... security. If you use HomeKit or not, you know that the hardware and encryption is certified to be extremely extremely secure, who wouldnt want that for all their home automation.
Overall, I think that from a cost/features perspective, those looking at the Nest should also look at the ecobee. It was definitely the right decision for me.