Whatever stack you are most comfortable using.

If all your integrations with AI are via HTTP API's then it does not matter what stack you choose, they all can call API's. Maybe some stacks will have pre-built libraries but really, AI like cursor, copilot or chatgpt can create an AI HTTP API library if that's what you're doing. If you are building AI/ML yourself then you'll have narrower choices of stacks.

If you choose a stack that is widespread and has been around for years, like ROR or python/django, then chances are AI will be better trained to be your helpful assistant that is sometimes wrong.