AllWinner parts are not bad if, and only if, the features you need are already clearly supported. Don’t invest in an AllWinner-based design expecting to implement key SoC features later. If it doesn’t work right now, there’s no guarantee it will ever be supported.

That said, upstream support for AllWinner parts has come a long way and continues to improve. I wouldn’t mind using them in certain projects.

However, anyone who absolutely needs good documentation and SoC support needs to stick with a vendor that emphasizes openness and good documentation. NXP i.MX is the safe choice.