Start with 3. Most of the complaints you see on Hacker News are from people who have a large existing codebase in 2.x that they'd need to migrate over, or who need to use an esoteric library that hasn't been ported over. It will probably never make sense for these people to migrate; they have a large fixed cost to update their software, and the benefits won't outweigh them for a long time. You don't have that cost, so you might as well enjoy the benefits.