Assuming you'd prioritise raw performance over portability and battery life, I'd recommend the
It's a workstation laptop configurable to have a 512 GB NVMe SSD.
The CPU is an Intel Xeon E3-1505M v5, a quad core, hyperthreaded CPU, with base clock of 2.8 GHz and turbo up to 3.7 GHz (4 core turbo would be 3.5 GHz), it is one of the most powerful mobile CPUs currently on the market.
If you plan on heavily utilising the Intel graphics, or a large L4 cache appeals to you, then you can upgrade to the E3-1545M v5, with GT4e graphics, and the associated 128 MB of eDRAM on die.
In the default configuration, the laptop comes with Windows 10 Pro preinstalled, but you could choose to forgo that. With Ubuntu preinstalled, you save the licence price of $94. Note though, that they install Ubuntu 14.04 LTS, not the latest 16.04 LTS or 16.10.
The laptop also comes with a Quadro M2000M. While a Quadro specifically isn't necessary, its 640 CUDA cores and 4 GB of VRAM make it well suited for accelerating TensorFlow using cuDNN.
RAM starts at 32 GB and is upgradable up to 64 GB. Upgrading to ECC RAM is also an option. Note that laptop OEMs tend to overcharge for RAM upgrades, so you might be better off purchasing your own, if you wanted more.
The display is a fairly mediocre 1080p one. You might choose to upgrade to 4K, or a wider gamut panel, add a camera or remove the microphone.
You might also like to upgrade to a backlit keyboard ($33), a higher capacity battery, add a second hard drive and/or add a RAID card.
To summarise: The Dell Precision is a highly customisable and powerful mobile workstation. It should take care of anything you throw at it with speed, and it also supports Ubuntu (optionally preinstalled).