There is ton of new interesting libraries being compatible with Python 3 only, so you can make this argument in either way. In the end, you should ask yourself

There is ton of new interesting libraries being compatible with Python 3 only, so you can make this argument in either way. In the end, you should ask yourself some questions: Am I starting a new project or continuing an older one? If the former one, Python 3 should be preferred unless some library I need is only available for Python 2. If the latter, I should ask if the cost of migrating my codebase makes sense. If not, Python 2 is still a viable choice until 2020 at least.