I think they're both barely better than useless, but the software for both is only going to improve. Amazon is going to hire the AI people and build up their own knowledgebase in the A9 team over the next few years, and Google is going to make the partnerships to reach third party skills parity over the next few months.
The right way to choose between them is by looking at the hardware, and the reviews I've seen say that the Echo Dot is too quiet. That can't be fixed in software.
The right way to choose between them is by looking at the hardware, and the reviews I've seen say that the Echo Dot is too quiet. That can't be fixed in software.